High-density plasma source

ABSTRACT

The present invention relates to a plasma source. The plasma source includes a cathode assembly having an inner cathode section and an outer cathode section. An anode is positioned adjacent to the outer cathode section so as to form a gap there between. A first power supply generates a first electric field across the gap between the anode and the outer cathode section. The first electric field ionizes a volume of feed gas that is located in the gap, thereby generating an initial plasma. A second power supply generates a second electric field proximate to the inner cathode section. The second electric field super-ionizes the initial plasma to generate a plasma comprising a higher density of ions than the initial plasma.

BACKGROUND OF INVENTION

[0001] Plasma is considered the fourth state of matter. A plasma is acollection of charged particles that move in random directions. A plasmais, on average, electrically neutral. One method of generating a plasmais to drive a current through a low-pressure gas between two conductingelectrodes that are positioned parallel to each other. Once certainparameters are met, the gas “breaks down” to form the plasma. Forexample, a plasma can be generated by applying a potential of severalkilovolts between two parallel conducting electrodes in an inert gasatmosphere (e.g., argon) at a pressure that is in the range of about10⁻¹ to 10⁻² Torr.

[0002] Plasma processes are widely used in many industries, such as thesemiconductor manufacturing industry. For example, plasma etching iscommonly used to etch substrate material and to etch films deposited onsubstrates in the electronics industry. There are four basic types ofplasma etching processes that are used to remove material from surfaces:sputter etching, pure chemical etching, ion energy driven etching, andion inhibitor etching.

[0003] Plasma sputtering is a technique that is widely used fordepositing films on substrates and other work pieces. Sputtering is thephysical ejection of atoms from a target surface and is sometimesreferred to as physical vapor deposition (PVD). Ions, such as argonions, are generated and are then drawn out of the plasma and acceleratedacross a cathode dark space. The target surface has a lower potentialthan the region in which the plasma is formed. Therefore, the targetsurface attracts positive ions.

[0004] Positive ions move towards the target with a high velocity andthen impact the target and cause atoms to physically dislodge or sputterfrom the target surface. The sputtered atoms then propagate to asubstrate or other work piece where they deposit a film of sputteredtarget material. The plasma is replenished by electron-ion pairs formedby the collision of neutral molecules with secondary electrons generatedat the target surface.

[0005] Reactive sputtering systems inject a reactive gas or mixture ofreactive gases into the sputtering system. The reactive gases react withthe target material either at the target surface or in the gas phase,resulting in the deposition of new compounds. The pressure of thereactive gas can be varied to control the stoichiometry of the film.Reactive sputtering is useful for forming some types of molecular thinfilms.

[0006] Magnetron sputtering systems use magnetic fields that are shapedto trap and concentrate secondary electrons proximate to the targetsurface. The magnetic fields increase the density of electrons and,therefore, increase the plasma density in a region that is proximate tothe target surface. The increased plasma density increases the sputterdeposition rate.

BRIEF DESCRIPTION OF DRAWINGS

[0007] This invention is described with particularity in the detaileddescription. The above and further advantages of this invention may bebetter understood by referring to the following description inconjunction with the accompanying drawings, in which like numeralsindicate like structural elements and features in various figures. Thedrawings are not necessarily to scale, emphasis instead being placedupon illustrating the principles of the invention.

[0008]FIG. 1 illustrates a cross-sectional view of a known plasmagenerating apparatus having a direct current (DC) power supply.

[0009]FIG. 2A illustrates a cross-sectional view of a plasma generatingapparatus having a segmented cathode according to the invention.

[0010]FIG. 2B illustrates a cross-sectional view of the segmentedcathode of FIG. 2A.

[0011]FIG. 3 illustrates a cross-sectional view of a plasma generatingapparatus including a magnet assembly according to the invention.

[0012]FIG. 4 illustrates a graphical representation of applied power asa function of time for periodic pulses applied to an initial plasma inthe plasma generating system of FIG. 2A.

[0013]FIG. 5 illustrates a cross-sectional view of a plasma generatingapparatus including the magnet assembly of FIG. 3 and an additionalmagnet assembly according to the invention.

[0014]FIG. 6 illustrates a cross-sectional view of a plasma generatingapparatus including the magnet assembly of FIG. 3 and an additionalmagnet assembly according to the invention.

[0015]FIG. 7 illustrates a cross-sectional view of another embodiment ofa plasma generating apparatus including a magnet assembly according tothe invention.

[0016]FIG. 8 illustrates a cross-sectional view of a plasma generatingapparatus including a magnet configuration that includes a first magnetand a second magnet according to the invention.

[0017]FIG. 9 illustrates a cross-sectional view of a plasma generatingapparatus according to the present invention including a segmentedcathode assembly, an ionizing electrode, and a first, a second and athird power supply.

[0018]FIG. 10 illustrates a cross-sectional view of a plasma generatingapparatus according to the present invention including a segmentedcathode assembly, a common anode, an ionizing electrode and a first, asecond and a third power supply.

[0019]FIG. 11 illustrates a cross-sectional view of a plasma generatingapparatus according to the present invention including a segmentedcathode assembly and a first, a second and a third power supply.

[0020]FIG. 12 illustrates a cross-sectional view of a plasma generatingapparatus according to the present invention including a segmentedcathode assembly, an excited atom source, and a first, and a secondpower supply.

[0021]FIG. 13 illustrates a graphical representation of the power as afunction of time for each of a first, a second and a third power supplyfor one mode of operating the plasma generating system of FIG. 9.

[0022]FIG. 14 illustrates a graphical representation of power generatedas a function of time for each of a first, a second and a third powersupply for one mode of operating the plasma generating system of FIG. 9.

[0023]FIG. 15 illustrates a graphical representation of the power as afunction of time for each of a first, a second and a third power supplyfor one mode of operating the plasma generating system of FIG. 9.

[0024]FIG. 16A through FIG. 16C are flowcharts of illustrative processesof generating high-density plasmas according to the present invention.

DETAILED DESCRIPTION

[0025]FIG. 1 illustrates a cross-sectional view of a known plasmagenerating apparatus 100 having a DC power supply 102. The known plasmagenerating apparatus 100 includes a vacuum chamber 104 where a plasma105 is generated. The vacuum chamber 104 can be coupled to ground. Thevacuum chamber 104 is positioned in fluid communication with a vacuumpump 106 via a conduit 108 and a valve 109. The vacuum pump 106 isadapted to evacuate the vacuum chamber 104 to high vacuum. The pressureinside the vacuum chamber 104 is generally less than 10⁻¹ Torr. A feedgas 110 from a feed gas source 111, such as an argon gas source, isintroduced into the vacuum chamber 104 through a gas inlet 112. The gasflow is controlled by a valve 113.

[0026] The plasma generating apparatus 100 also includes a cathodeassembly 114. The cathode assembly 114 is generally in the shape of acircular disk. The cathode assembly 114 can include a target 116. Thecathode assembly 114 is electrically connected to a first terminal 118of the DC power supply 102 with an electrical transmission line 120. Aninsulator 122 isolates the electrical transmission line 120 from a wallof the vacuum chamber 104. An anode 124 is electrically connected to asecond terminal 126 of the DC power supply 102 with an electricaltransmission line 127. An insulator 128 isolates the electricaltransmission line 127 from the wall of the vacuum chamber 104. The anode124 is positioned in the vacuum chamber 104 proximate to the cathodeassembly 114. An insulator 129 isolates the anode 124 from the cathodeassembly 114. The anode 124 and the second output 126 of the DC powersupply 102 are coupled to ground in some systems.

[0027] The plasma generating apparatus 100 illustrates a magnetronsputtering system that includes a magnet 130 that generates a magneticfield 132 proximate to the target 116. The magnetic field 132 isstrongest at the poles of the magnet 130 and weakest in the region 134.The magnetic field 132 is shaped to trap and concentrate secondaryelectrons proximate to the target surface. The magnetic field increasesthe density of electrons and, therefore, increases the plasma density ina region that is proximate to the target surface.

[0028] The plasma generating apparatus 100 also includes a substratesupport 136 that holds a substrate 138 or other work piece. Thesubstrate support 136 can be electrically connected to a first terminal140 of a RF power supply 142 with an electrical transmission line 144.An insulator 146 isolates the RF power supply 142 from a wall of thevacuum chamber 104. A second terminal 148 of the RF power supply 142 iscoupled to ground.

[0029] In operation, the feed gas 110 from the feed gas source 111 isinjected into the chamber 104. The DC power supply 102 applies a DCvoltage between the cathode assembly 114 and the anode 124 that causesan electric field 150 to develop between the cathode assembly 114 andthe anode 124. The amplitude of the DC voltage is chosen so that it issufficient to cause the resulting electric field to ionize the feed gas110 in the vacuum chamber 104 and to ignite the plasma 105.

[0030] The ionization process in known plasma sputtering apparatus isgenerally referred to as direct ionization or atomic ionization byelectron impact and can be described by the following equation:

Ar+e⁻→Ar⁺+2e⁻

[0031] where Ar represents a neutral argon atom in the feed gas 110 ande⁻ represents an ionizing electron generated in response to the voltageapplied between the cathode assembly 114 and the anode 124. Thecollision between the neutral argon atom and the ionizing electronresults in an argon ion (Ar⁺) and two electrons.

[0032] The plasma 10S is maintained, at least in part, by secondaryelectron emission from the cathode assembly 114. The magnetic field 132that is generated proximate to the cathode assembly 114 confines thesecondary electrons in the region 134 and, therefore, confines theplasma 105 approximately in the region 134. The confinement of theplasma in the region 134 increases the plasma density in the region 134for a given input power.

[0033] The plasma generating apparatus 100 can be configured formagnetron sputtering. Since the cathode assembly 114 is negativelybiased, ions in the plasma 105 bombard the target 116. The impact causedby these ions bombarding the target 116 dislodges or sputters materialfrom the target 116. A portion of the sputtered material forms a thinfilm of sputtered target material on the substrate 138.

[0034] Known magnetron sputtering systems have relatively poor targetutilization. The term “poor target utilization” is defined herein tomean undesirable non-uniform erosion of target material. Poor targetutilization is caused by a relatively high concentration of positivelycharged ions in the region 134 that results in a non-uniform plasma.Similarly, magnetron etching systems (not shown) typically haverelatively non-uniform etching characteristics.

[0035] Increasing the power applied to the plasma can increase theuniformity and density of the plasma. However, increasing the amount ofpower necessary to achieve even an incremental increase in uniformityand plasma density can significantly increase the probability ofestablishing an electrical breakdown condition leading to an undesirableelectrical discharge (an electrical arc) in the chamber 104.

[0036] Applying pulsed direct current (DC) to the plasma can beadvantageous since the average discharge power can remain relatively lowwhile relatively large power pulses are periodically applied.Additionally, the duration of these large voltage pulses can be presetso as to reduce the probability of establishing an electrical breakdowncondition leading to an undesirable electrical discharge. An undesirableelectrical discharge will corrupt the plasma process and can causecontamination in the vacuum chamber 104. However, very large powerpulses can still result in undesirable electrical discharges regardlessof their duration.

[0037] In one embodiment, an apparatus according to the presentinvention generates a plasma having a higher density of ions for agiving input power than a plasma generated by known plasma systems, suchas the plasma generating apparatus 100 of FIG. 1.

[0038] A high-density plasma generation method and apparatus accordingto the present invention uses an electrode structure including three ormore electrodes to generate a high-density plasma including excitedatoms, ions, neutral atoms and electrons. The electrodes can be acombination of cathodes, anodes, and/or ionizing electrodes. Theelectrodes can be configured in many different ways, such as a ringelectrode structure, a linear electrode structure, or hollow cathodeelectrode structure. The plasma generation method and apparatus of thepresent invention provides independent control of two or moreco-existing plasmas in the system.

[0039] A high-density plasma source according to the present inventioncan include one or more feed gas injection systems that inject feed gasproximate to one or more of the electrodes in the plasma source. Thefeed gas can be any mixture of gases as described herein. The one ormore feed gas injection systems can also inject plasma proximate to oneor more of the electrodes in the plasma source. The injected plasma canbe a high-density plasma or a low-density plasma. In one embodiment, aninitial plasma is generated and then it is super-ionized to form ahigh-density plasma. The term “super-ionized” is defined herein to meanthat at least 75% of the neutral atoms in the plasma are converted toions.

[0040] The high-density plasma source of the present invention canoperate in a constant power, constant voltage, or constant current mode.These modes of operation are discussed herein. In addition, thehigh-density plasma source can use different types of power supplies togenerate the high-density plasma. For example, direct-current (DC),alternating-current (AC), radio-frequency (RF), or pulsed DC powersupplies can be used to generate the high-density plasma. The powersupplies can generate power levels in the range of about 1 W to 10 MW.

[0041] The plasma generated by the high-density plasma source of thepresent invention can be used to sputter materials from solid or liquidtargets. Numerous types of materials can be sputtered. For example,magnetic, non-magnetic, dielectric, metals, and semiconductor materialscan be sputtered.

[0042] In one embodiment, the high-density plasma source of the presentinvention generates relatively high deposition rates near the outer edgeof a sputtering target. The target can be designed and operated suchthat the increase in the deposition rate near the outer edge of thesputtering target compensates for the decrease of the sputtering ratetypically associated with the edge of a sputtering target. Thisembodiment allows the use of relatively small targets, which can reducethe overall footprint of a process tool, the cost of the target and thecost to operate the process tool.

[0043] The high-density plasma source of the present invention provideshigh target utilization and high sputtering uniformity. Additionally,the plasma generated by the high-density plasma source of the presentinvention can be used for producing ions or atoms from molecules fornumerous applications, such as sputter etch, reactive etch, chemicalvapor deposition, and for generating ion beams.

[0044]FIG. 2A illustrates a cross-sectional view of a plasma generatingapparatus 200 having a segmented cathode 202 according to the invention.In one embodiment, the segmented cathode 202 includes an inner cathodesection 202 a and an outer cathode section 202 b. In some embodiments(not shown), the segmented cathode 202 includes more than two sections.The segmented cathode 202 can be composed of a metal material, such asstainless steel or any other material that does not chemically reactwith reactive gases. The segmented cathode 202 can include a target (notshown) that is used for sputtering. The inner cathode section 202 a andthe outer cathode section 202 b can be composed of different materials.

[0045] The outer cathode section 202 b is coupled to a first output 204of a first power supply 206. The first power supply 206 can operate in aconstant power mode. The term “constant power mode” is defined herein tomean that the power generated by the power supply has a substantiallyconstant power level regardless of changes in the output current and theoutput voltage level. In another embodiment, the first power supply 206operates in a constant voltage mode. The term “constant voltage mode” isdefined herein to mean that the voltage generated by the power supplyhas a substantially constant voltage level regardless of changes in theoutput current and the output power level. The first power supply 206can include an integrated matching unit (not shown). Alternatively, amatching unit (not shown) can be electrically connected to the firstoutput 204 of the first power supply 206.

[0046] A second output 208 of the first power supply 206 is coupled to afirst anode 210. An insulator 211 isolates the first anode 210 from theouter cathode section 202 b. In one embodiment, the second output 208 ofthe first power supply 206 and the first anode 210 are coupled to groundpotential (not shown).

[0047] In one embodiment (not shown), the first output 204 of the firstpower supply 206 couples a negative voltage impulse to the outer cathodesection 202 b. In another embodiment (not shown), the second output 208of the first power supply 206 couples a positive voltage impulse to thefirst anode 210. Numerous types of power supplies can be used for thefirst power supply 206. For example, the first power supply 206 can be apulsed power supply, radio-frequency (RF) power supply, analternating-current (AC) power supply, or a direct-current (DC) powersupply.

[0048] The first power supply 206 can be a pulsed power supply thatgenerates peak voltage levels of up to about 5 kV. Typical operatingvoltages are in the range of about 50V to 5 kV. The first power supply206 can generate peak current levels in the range of about 1 mA to 100kA depending on the desired volume and characteristics of the plasma.Typical operating currents vary from less than one hundred amperes tomore than a few thousand amperes depending on the desired volume andcharacteristics of the plasma. The first power supply 206 can generatepulses having a repetition rate that is below 1 kHz. The first powersupply 206 can generate pulses having a pulse width that is in the rangeof about one microsecond to several seconds.

[0049] The first anode 210 is positioned so as to form a gap 212 betweenthe first anode 210 and the outer cathode section 202 b that issufficient to allow current to flow through a region 214 between thefirst anode 210 and the outer cathode section 202 b. In one embodiment,the width of the gap 212 is in the range of about 0.3 cm to 10 cm. Thesurface area of the outer cathode section 202 b determines the volume ofthe region 214. The gap 212 and the total volume of the region 214 areparameters in the ionization process as described herein.

[0050] For example, the gap 212 can be configured to generate exitedatoms from ground state atoms. The excited atoms can increase thedensity of a plasma. Since excited atoms generally require less energyto ionize than ground state gas atoms, a volume of excited atoms cangenerate a higher density plasma than a similar volume of ground statefeed gas atoms for the same input energy. Additionally, the gap 212 canbe configured to conduct exited atoms towards the inner cathode section202 a. The excited atoms can either be generated externally or insidethe gap 212 depending on the configuration of the system. In oneembodiment, the gap 212 exhibits a pressure differential that forces theexited atoms towards the inner cathode section 202 a. This can increasethe density of the plasma proximate to the inner cathode section 202 aas previously discussed.

[0051] The gap 212 can be a plasma generator. In this configuration,feed gas is supplied to the gap 212 and a plasma is ignited in the gap212. An ignition condition in the gap 212 can be optimized by varyingcertain parameters of the gap 212. For example, the presence of crossedelectric and magnetic fields in the gap 212 can assist in the ignitionand development of a plasma in the gap 212. The crossed electric andmagnetic fields trap electrons and ions, thereby improving theefficiency of the ionization process.

[0052] The gap 212 can facilitate the use of high input power. Forexample, as high power is applied to a plasma that is ignited anddeveloping in the gap 212, additional feed gas can be supplied to thegap 212. This additional feed gas displaces some of the alreadydeveloping plasma and absorbs any excess power applied to the plasma.The absorption of the excess power prevents the plasma from contractingand terminating which could otherwise occur without the additional feedgas.

[0053] In some embodiments (not shown), the first anode 210 and/or theouter cathode section 202 b can include raised areas, depressed areas,surface anomalies, or shapes that improve the ionization process. Forexample, the pressure in the region 214 can be optimized by including araised area (not shown) on the surface of the outer cathode section 202b. The raised area can create a narrow passage at a location in theregion 214 between the first anode 210 and the outer cathode section 202b that changes the pressure in the region 214.

[0054] The first output 220 of a second power supply 222 is electricallycoupled to the inner cathode section 202 a. The second power supply 222can operate in a constant power mode or a constant voltage mode. Thesecond power supply 222 can have an integrated matching unit (notshown). Alternatively, a matching unit (not shown) is electricallyconnected to the first output 220 of the first power supply 222. Thesecond power supply 222 can be any type of power supply, such as apulsed power supply, a DC power supply, an AC power supply, or a RFpower supply.

[0055] A second output 224 of the second power supply 222 is coupled toa second anode 226. An insulator 227 is positioned to isolate the secondanode 226 from the outer cathode section 202 b. Another insulator (notshown) can be positioned to isolate the second anode 226 from the innercathode section 202 a. In one embodiment (not shown), the second output224 of the second power supply 222 and the second anode 226 areelectrically connected to ground potential.

[0056] The first output 220 of the second power supply 222 can couple anegative voltage impulse to the inner cathode section 202 a. The secondoutput 224 of the second power supply 222 can couple a positive voltageimpulse to the second anode 226.

[0057] The second power supply 222 can be a pulsed power supply thatgenerates peak voltage levels in the range of about 50V to 5 kV. Thesecond power supply 222 can generate peak current levels in the range ofabout 1 mA to 100 kA depending on the desired volume and characteristicsof the plasma. Typical operating currents varying from less than onehundred amperes to more than a few thousand amperes depending on thedesired volume and characteristics of the plasma and the desired plasmadensity. The pulses generated by the second power supply 222 can have arepetition rate that is below 1 kHz. The pulse width of the pulsesgenerated by the second power supply 222 can be between about onemicrosecond and several seconds.

[0058] The second anode 226 is positioned proximate to the inner cathodesection 202 a such that current is capable of flowing between the secondanode 226 and the inner cathode section 202 a. The distance between thesecond anode 226 and the inner cathode section 202 a can be in the rangeof about 0.3 cm to 10 cm.

[0059] The plasma generating apparatus 200 can include a chamber (notshown), such as a vacuum chamber. The chamber is coupled in fluidcommunication to a vacuum pump (not shown) through a vacuum valve (notshown). The chamber can be electrically coupled to ground potential.

[0060] One or more gas lines 230, 232 provide feed gas 234, 236(indicated by arrows) from one or more feed gas sources 238, 240,respectively, to the chamber. The feed gas lines 230, 232 can includein-line gas valves 242, 244 that can control the gas flow to thechamber. The gas lines 230, 232 can be isolated from the chamber andother components by insulators (not shown). The gas lines 230, 232 canbe isolated from the one or more feed gas sources 238, 240 using in-lineinsulating couplers (not shown). The one or more feed gas sources 238,240 can include any feed gas, such as argon. The feed gas can be amixture of different gases, reactive gases, or pure reactive gas gases.The feed gas can include a noble gas or a mixture of gases.

[0061] In one embodiment, the in-line gas valves 242, 244 are switchablemass flow controllers (not shown). The switchable mass flow controllerscan be programmed inject the feed gases 234, 236 in a pulsed manner fromthe feed gas sources 238, 240, respectively. For example, the pressurein the gap 212 can be varied and optimized by pulsing the feed gas 234that is injected directly into the gap 212. In one embodiment, thetiming of the pulses is synchronized to the timing of power pulsesgenerated by the first power supply 206 operated in a pulsed mode.Pulsing the feed gases 234, 236 can also assist in the generation ofexcited atoms including metastable atoms in the gap 212. For example, bypulsing the feed gas 234 in the gap 212, the instantaneous pressure inthe gap is increased while the average pressure in the chamber isunchanged.

[0062] Skilled artisans will appreciate that the plasma generatingapparatus 200 can be operated in many different modes. In some modes ofoperation, the first 206 and the second power supplies 222 together withthe segmented cathode 202 are used to generate independent plasmas. Theparameters of an initial plasma and a high-density plasma can be variedindividually as required by the particular plasma process.

[0063] In one mode of operation, the feed gas 234 from the feed gassource 238 is supplied to the chamber by controlling the gas valve 242.The feed gas 234 is supplied between the outer cathode section 202 b andthe first anode 210. The feed gas 234 can be directly injected into thegap 212 between the outer cathode section 202 b and the first anode 210in order to increase the density of a plasma that is generated in thegap 212. Increasing the flow rate of the feed gas causes a rapid volumeexchange in the region 214 between the outer cathode section 202 b andthe first anode 210. This rapid volume exchange increases the maximumpower that can be applied across the gap 212 and thus, permits ahigh-power pulse having a relatively long duration to be applied acrossthe gap 212. Applying high-power pulses having relatively long durationsacross the gap 212 results in the formation of high-density plasmas inthe region 214, as described herein.

[0064] In another mode of operation, the first power supply 206 is acomponent in an ionization source that generates an initial or apre-ionization plasma in the region 214. The pre-ionization plasma canbe a weakly-ionized plasma. The term “weakly-ionized plasma” is definedherein to mean a plasma with a relatively low peak plasma density. Thepeak plasma density of the weakly ionized plasma depends on theproperties of the specific plasma processing system. For example, aweakly ionized argon plasma is a plasma that has a peak plasma densitythat is in the range of about 10⁷ to 10¹² cm⁻³.

[0065] After a sufficient volume of the feed gas 234 is supplied betweenthe outer cathode section 202 b and the first anode 210, the first powersupply 206 applies a voltage between the outer cathode section 202 b andthe first anode 210. The first power supply 206 can be a pulsed (DC)power supply that applies a negative voltage pulse to the outer cathodesection 202 b. The size and shape of the voltage pulse are chosen suchthat an electric field 250 (FIG. 2B) develops between the outer cathodesection 202 b and the first anode 210. The first power supply can be aDC, AC, or a RF power supply.

[0066] The amplitude and shape of the electric field 250 are chosen suchthat an initial plasma is generated in the region 214 between the firstanode 210 and the outer cathode section 202 b. The initial plasma can bea weakly-ionized plasma that is used for pre-ionization and generallyhas a relatively low-level of ionization, as described herein. In oneembodiment, the first power supply 206 generates a low power pulsehaving an initial voltage that is in the range of about 100V to 5 kVwith a discharge current that is in the range of about 0.1 A to 100 A.The width of the pulse can be in the range of approximately 0.1microseconds to one hundred seconds. Specific parameters of the pulseare discussed herein in more detail.

[0067] In another mode of operation, prior to the generation of theinitial plasma in the region 214, the first power supply 206 generates apotential difference between the outer cathode section 202 b and thefirst anode 210 before the feed gas 234 is supplied to the region 214.In this mode of operation, the feed gas 234 is ignited once a sufficientvolume of feed gas is present in the region 214.

[0068] In yet another mode of operation, a direct current (DC) powersupply (not shown) is used in an ionization source to generate andmaintain the initial plasma in the region 214. In this mode ofoperation, the DC power supply is adapted to generate a voltage that islarge enough to ignite the initial plasma. For example, the DC powersupply can generate an initial voltage of several kilovolts that createsa plasma discharge voltage that is in the range of about 100V to 1 kVwith a discharge current that is in the range of about 0.1 A to 100 A.The value of the discharge current depends on the power level of the DCpower supply and is a function of the volume and characteristics of theplasma. Furthermore, the presence of a magnetic field (not shown) in theregion 214 can have a dramatic effect on the value of the appliedvoltage and current that is required to generate the initial plasma.

[0069] The DC power supply can generate a current that is in the rangeof about 1 mA to 100 A depending on the volume of the plasma and thestrength of a magnetic field in a region 214. In one embodiment, beforegenerating the initial plasma, the DC power supply is adapted togenerate and maintain an initial peak voltage potential between theouter cathode section 202 b and the first anode 210 before theintroduction of the feed gas 234.

[0070] In still another mode of operation, an alternating current (AC)power supply (not shown) is used to generate and maintain the initialplasma in the region 214. An AC power supply can require less power togenerate and maintain a plasma than a DC power supply. In other modes ofoperation, the initial plasma can be generated and maintained using aplanar discharge source, a radio frequency (RF) diode source, anultraviolet (UV) source, an X-ray source, an electron beam source, anion beam source, an inductively coupled plasma (ICP) source, acapacitively coupled plasma (CCP) source, a microwave plasma source, anelectron cyclotron resonance (ECR) source, a helicon plasma source, orionizing filament techniques. In some of these modes of operation, aninitial plasma can be formed outside of the region 214 and then diffusedinto the region 214.

[0071] Forming an initial plasma in the region 214 substantiallyeliminates the probability of establishing a breakdown condition in thechamber when high-power pulses are subsequently applied between theouter cathode section 202 b and the first anode 210. The probability ofestablishing a breakdown condition is substantially eliminated becausethe initial plasma has at least a low-level of ionization that provideselectrical conductivity through the plasma. This conductivitysubstantially prevents the setup of a breakdown condition, even whenhigh-power is applied to the plasma.

[0072] Referring back to FIG. 2A, the initial plasma diffuses somewhathomogeneously through the region 252 as additional feed gas 234 isinjected into the region 214. The additional feed gas 234 forces theinitial plasma from the region 214 into the region 252. This homogeneousdiffusion tends to facilitate the creation of a highly uniform plasma inthe region 252. In one embodiment, the pressure in the region 214 ishigher than the pressure in the region 252. This pressure gradientcauses the initial plasma in the region 214 to diffuse into the region252.

[0073] Once an initial plasma is formed, several modes of operation canbe realized. For example, in one mode of operation, the first powersupply 206 generates high-power pulses in the gap 212 between the outercathode section 202 b and the first anode 210. The desired power levelof the high-power pulses depends on several factors including thedesired volume and characteristics of the plasma as well as the densityof the initial plasma. In one embodiment, the power level of thehigh-power pulse is in the range of about 1 kW to 10 MW.

[0074] Each of the high-power pulses is maintained for a predeterminedtime that can be in the range of about one microsecond to ten seconds.The repetition frequency or repetition rate of the high-power pulses canbe in the range of about 0.1 Hz to 1 kHz. The average power generated bythe first power supply 206 can be less than one megawatt depending onthe characteristics and the volume of the plasma. The thermal energy inthe outer cathode section 202 b and/or the first anode 210 can beconducted away or dissipated by liquid or gas cooling such as heliumcooling (not shown).

[0075] The high-power pulses generate an electric field 250 (FIG. 2B)between the outer cathode section 202 b and the first anode 210. Theelectric field 250 can be a relatively strong electric field, dependingon the strength and duration of the high-power pulses. The electricfield 250 is substantially located in the region 214 between the outercathode section 202 b and the first anode 210. The electric field 250can be a static or a pulsed electric field. In another embodiment, theelectric field 250 is a quasi-static electric field. The term“quasi-static electric field” is defined herein to mean an electricfield that has a characteristic time of electric field variation that ismuch greater than the collision time for electrons with neutral gasparticles. Such a time of electric field variation can be on the orderof ten seconds. In another embodiment, the electric field can be analternating electric field. The term “alternating electric field” isdefined herein to mean that the polarity of the electric field changeswith time. The strength and the position of the electric field 250 arediscussed in more detail herein.

[0076] The high-power pulses generate a high-density plasma from theinitial plasma. The term “high-density plasma” is also referred to as a“strongly-ionized plasma.” The terms “high-density plasma” and“strongly-ionized plasma” are defined herein to mean a plasma with arelatively high peak plasma density. For example, the peak plasmadensity of the high-density plasma is greater than about 10¹² cm⁻³. Thedischarge current that is formed from the high-density plasma can be onthe order of about 5 kA with a discharge voltage that is in the range ofabout 50V to 500V for a pressure that is in the range of about 5 mTorrto 10 Torr.

[0077] The high-density plasma tends to diffuse homogenously in theregion 252. The homogenous diffusion creates a more homogeneous plasmavolume. The pressure gradient responsible for this homogenous diffusionis described in more detail herein. Homogeneous plasma volumes areadvantageous for many plasma processes. For example, plasma etchingprocesses using homogenous plasma volumes accelerate ions in thehigh-density plasma towards the surface of the substrate (not shown)being etched in a more uniform manner than conventional plasma etching.Consequently, the surface of the substrate is etched more uniformly.Plasma processes using homogeneous plasma volumes can achieve highuniformity without the necessity of rotating the substrate.

[0078] Magnetron sputtering systems using homogenous plasma volumesaccelerate ions in the high-density plasma towards the surface of thesputtering target in a more uniform manner than conventional magnetronsputtering. Consequently, the target material is deposited moreuniformly on a substrate without the necessity of rotating the substrateand/or the magnetron. Also, the surface of the sputtering target iseroded more evenly and, thus higher target utilization is achieved. Inone embodiment, target material can be applied to the first 210 and/orthe second anode 226 to reduce possible contamination from sputteringundesired material.

[0079] Referring back to FIG. 2A, the second power supply 222 can be apulsed power supply that generates high-power pulses between the innercathode section 202 a and the second anode 226 after the high-densityplasma is formed in the region 214 and diffuses into the region 252proximate to the inner cathode section 202 a. The desired power level ofthe high-power pulses depends on several factors including the volumeand other characteristics of the plasma such as the density of thehigh-density plasma. In one embodiment, the power level of thehigh-power pulse is in the range of about 1 kW to 10 MW.

[0080] Each of the high-power pulses is maintained for a predeterminedtime that can be in the range of one microsecond to ten seconds. Therepetition frequency or repetition rate of the high-power pulses can bein the range of between about 0.1 Hz and 1 kHz. The average powergenerated by the second power supply 222 can be less than one megawattdepending on the desired volume and characteristics of the plasma. Thethermal energy in the inner cathode section 202 a and/or the secondanode 226 can be conducted away or dissipated by liquid or gas coolingsuch as helium cooling (not shown).

[0081] The high-power pulses generate an electric field 254 (FIG. 2B)between the inner cathode section 202 a and the second anode 226. Theelectric field 254 can be a pulsed electric field, a quasi-staticelectric field or an alternating electric field. The strength and theposition of the electric field 254 will be discussed in more detailherein.

[0082] The second power supply 222 generates high power pulses thatlaunch additional power into the already strongly ionized plasma and,therefore, super-ionize the high-density plasma in the region 252. Thedischarge current can be on the order of 5 kA with a discharge voltagethat is in the range of about 50V to 500V for a pressure that is in therange of about 5 mTorr to 10 Torr.

[0083] In another mode of operation, an initial plasma is generated inthe region 214 and the initial plasma diffuses to the region 252 asadditional feed gas is supplied to the region 214.

[0084] In this mode of operation, the gap 212 is dimensioned to create apressure differential between the region 214 and the region 252. Thepressure differential forces the initial plasma that is generated in theregion 214 into the region 252. In this embodiment, the second powersupply 222 applies high-power pulses between the inner cathode section202 a and the second anode 226 after a suitable volume of initial plasmais present in the region 252. The high-power pulses create an electricfield 254 between the inner cathode section 202 b and the second anode226 that strongly-ionizes the initial plasma thereby creating ahigh-density plasma in the region 252.

[0085] In yet another mode of operation, feed gas 236 from the feed gassource 240 flows between the second anode 226 and the inner cathodesection 202 a at various times during the plasma generation process.This additional feed gas 236 can be a noble gas, a reactive gas, or amixture of gases. The additional feed gas 236 can facilitate a moreefficient plasma generation process and/or can result in a higherdensity plasma.

[0086] In still another mode of operation, a voltage generated by thesecond power supply 222 is sufficient to ignite a second plasma (notshown) from the feed gas 236 in the region 255 between the second anode226 and the inner cathode section 202 a. This second plasma flows fromthe region 255 into the region 252 as the second plasma is displaced bymore feed gas 236. Additionally, the second plasma from the region 255can commingle with the initial plasma from the region 214 in the region252. In one embodiment, a plasma diverting plate 256 (FIG. 2B) isdisposed proximate to the second anode 226 to divert the second plasmafrom the region 255 toward the inner cathode section 202 a and/ortowards the region 214. The size, shape, and location of the plasmadiverting plate 256 depend on the desired plasma properties of thesecond plasma. In one embodiment, target material can be applied to theplasma diverting plate 256 to reduce possible contamination fromsputtering undesired material.

[0087] Controlling the flow of the feed gases 234, 236 through theregions 214, 255, respectively, can affect the homogeneity, distributionprofile, and density of the plasma. Additionally, controlling certainparameters, such as power and pulse rate of the first 206 and the secondpower supplies 222 (FIG. 2A) can also affect the homogeneity,distribution profile, and density of the plasma.

[0088] The plasma generating apparatus 200 of the present inventiongenerates a relatively high electron temperature plasma and a relativelyhigh-density plasma. One application for the high-density plasma of thepresent invention is ionized physical vapor deposition (IPVD) (notshown), which is a technique that converts neutral sputtered atoms intopositive ions to enhance a sputtering process.

[0089]FIG. 2B illustrates a cross-sectional view of the segmentedcathode of FIG. 2A. Specifically, FIG. 2B shows that one or both of theelectric fields 250, 254 can facilitate a multi-step ionization processof the feed gases 234, 236, respectively, that substantially increasesthe rate at which the high-density plasma is formed. At least one of thefeed gases 234, 236 can be a molecular gas. The electric fields 250, 254enhance the formation of ions in the plasma. The multi-step or stepwiseionization process is described as follows with reference to theelectric field 250 between the outer cathode section 202 b and the firstanode 210.

[0090] A pre-ionizing voltage is applied between the outer cathodesection 202 b and the first anode 210 across the feed gas 234 to form aninitial plasma. The initial plasma can be a weakly-ionized plasma aspreviously discussed. The initial plasma is generally formed in theregion 214 and diffuses or is transported to the region 252 as the feedgas 234 continues to flow. In one embodiment (not shown), a magneticfield is generated in the region 214 and extends proximate to the centerof the inner cathode section 202 a. This magnetic field tends to assistin diffusing electrons in the initial plasma from the region 214 to theregion 252. The electrons in the initial plasma are substantiallytrapped in the region 252 by the magnetic field. The volume of initialplasma in the region 214 can be rapidly exchanged with a new volume offeed gas 234.

[0091] After the formation of the initial plasma in the region 214, thefirst power supply 206 (FIG. 2A) applies a high-power pulse between theouter cathode section 202 b and the first anode 210. This high-powerpulse generates the electric field 250 in the region 214. The electricfield 250 results in collisions occurring between neutral atoms,electrons, and ions in the initial plasma. These collisions generatenumerous excited atoms in the initial plasma. The excited atoms caninclude atoms that are in a metastable state.

[0092] The accumulation of excited atoms in the initial plasma altersthe ionization process. The electric field 250 can be a strong electricfield that facilitates a multi-step ionization process of an atomic feedgas that significantly increases the rate at which the high-densityplasma is formed. The multi-step ionization process has an efficiencythat increases as the density of excited atoms in the initial plasmaincreases. The strong electric field 250 enhances the formation of ionsof a molecular or atomic feed gas.

[0093] In one embodiment, the dimensions of the gap 212 between theouter cathode section 202 b and the first anode 210 are chosen so as tomaximize the rate of excitation of the atoms. The value of the electricfield 250 in the region 214 depends on the voltage level applied by thefirst power supply 206 and the dimensions of the gap 212. In someembodiments, the strength of the electric field 250 can be in the rangeof about 2V/cm to 10⁵V/cm depending on various system parameters andoperating conditions of the plasma system.

[0094] The size of the gap 212 can be in the range of about 0.30 cm to10 cm depending on various parameters of the desired plasma. In oneembodiment, the electric field 250 in the region 214 is rapidly appliedto the initial plasma. The rapidly applied electric field 250 can begenerated by applying a voltage pulse having a rise time that is in therange of about 0.1 microsecond to ten seconds.

[0095] In one embodiment, the dimensions of the gap 212 and theparameters of the applied electric field 250 are varied in order todetermine the optimum condition for a relatively high rate of excitationof the atoms in the region 214. Since an argon atom requires energy ofabout 11.55 eV to become excited, the applied electric field 250 can beadjusted to maximize the excitation rate of the argon atoms. As argonfeed gas 234 flows through the region 214, the initial plasma is formedand many of the atoms in the initial plasma then become excited by theapplied electric field 250. Thus, the vast majority of ground state feedgas atoms are not directly ionized, but instead undergo a stepwiseionization process.

[0096] The excited atoms in the initial plasma then encounter electronsthat are in the region 214. In the case of argon feed case, excitedargon atoms only require about 4 eV of energy to ionize while argonground state atoms require about 15.76 eV of energy to ionize.Therefore, when energy is applied in the region 214, the excited atomswill ionize at a much higher rate than the ground state atoms. Ions inthe high-density plasma strike the outer cathode section 202 b causingsecondary electron emission from the outer cathode section 202 b. Thesesecondary electrons interact with neutral or excited atoms in thehigh-density plasma. This process further increases the density of ionsin the high-density plasma as the feed gas 234 is exchanged.

[0097] The multi-step ionization process corresponding to the rapidapplication of the electric field 250 can be described as follows:

Ar+e⁻→Ar*+e⁻

Ar*+e⁻→Ar⁺+2e⁻

[0098] where Ar represents a neutral ground state argon atom in the feedgas 234 and e⁻ represents an ionizing electron generated in response toan initial plasma, when sufficient voltage is applied between the outercathode section 202 b and the first anode 210. Additionally, Ar*represents an excited argon atom in the initial plasma. The collisionbetween the excited argon atom and the ionizing electron results in anargon ion (Ar⁺) and two electrons.

[0099] As previously discussed, the excited argon atoms generallyrequire less energy to become ionized than neutral ground state argonatoms. Thus, the excited atoms tend to more rapidly ionize near thesurface of the outer cathode section 202 b than the neutral ground stateargon atoms. As the density of the excited atoms in the plasmaincreases, the efficiency of the ionization process rapidly increases.This increased efficiency eventually results in an avalanche-likeincrease in the density of the high-density plasma. Under appropriateexcitation conditions, the proportion of the energy applied to theinitial plasma, which is transformed to the excited atoms, is very highfor a pulsed discharge in the feed gas 234.

[0100] In one mode of operation, the density of the plasma is increasedby controlling the flow of the feed gas 234 in the region 214. In thisembodiment, a first volume of feed gas 234 is supplied to the region214. The first volume of feed gas 234 is then ionized to form an initialplasma in the region 214. The first power supply 206 then applies ahigh-power electrical pulse across the initial plasma. The high-powerelectrical pulse generates a high-density plasma from the initialplasma.

[0101] In another mode of operation, the feed gas 234 continues to flowinto the region 214 after the initial plasma is formed. The initialplasma is displaced or transported into the region 252 by a new volumeof feed gas 234. The second power supply 222 (FIG. 2A) then applies ahigh-power electrical pulse between the inner cathode section 202 a andthe second anode 226.

[0102] The density of the plasma is generally limited by the level andduration of the high-power electrical pulse that can be absorbed beforethe discharge contracts and terminates. Increasing the flow rate of atleast one of the feed gases 234, 236 can increase the level and durationof the high-power electrical pulse that can be absorbed by thedischarge. Any type of gas exchange means can be used to rapidlyexchange the volume of feed gas.

[0103] Thus, the density of the plasma can be increased by transportingthe initial plasma through the region 214 by a rapid volume exchange offeed gas 234. As the feed gas 234 moves through the region 214 andinteracts with the moving initial plasma, it becomes partially ionizedfrom the applied electrical pulse. Applying a high-power electricalpulse through the region 214 can result in an ionization process thatincludes a combination of direct ionization and/or stepwise ionizationas described herein. Transporting the initial plasma through the region214 by a rapid volume exchange of the feed gas 234 increases the leveland the duration of the power that can be applied to the high-densityplasma and, thus, generates a higher density strongly-ionized plasma.

[0104] In one embodiment, the plasma generating system 200 can beconfigured for plasma etching. In another embodiment, the plasmagenerating system 200 can be configured for plasma sputtering. Inparticular, the plasma generating system 200 can be configured forsputtering magnetic materials. Known magnetron sputtering systemsgenerally are not suitable for sputtering magnetic materials because themagnetic field generated by the magnetron can be absorbed by themagnetic target material. RF diode sputtering is sometimes used tosputter magnetic materials. However, RF diode sputtering generally haspoor film thickness uniformity and produces relatively low depositionrates.

[0105] The plasma generating system 200 can be adapted to sputtermagnetic materials by including a target assembly (not shown) having amagnetic target material and by driving that target assembly with an RFpower supply (not shown). For example, an RF power supply can provide anRF power that is about 10 kW. A substantially uniform initial plasma canbe generated by applying RF power across a feed gas that is locatedproximate to the target assembly. The high-density plasma is generatedby applying a strong electric field across the initial plasma asdescribed herein. The RF power supply applies a negative voltage bias tothe target assembly. Ions in the high-density plasma bombard the targetmaterial thereby causing sputtering.

[0106] The plasma generating system 200 can also be adapted to sputterdielectric materials. Dielectric materials can be sputtered by driving atarget assembly (not shown) including a dielectric target material withan RF power supply (not shown). For example, an RF power supply canprovide an RF power that is about 10 kW. A substantially uniform initialplasma can be generated by applying RF power across a feed gas that islocated proximate to the target assembly.

[0107] In one embodiment, a magnetic field is generated proximate to thetarget assembly in order to trap electrons in the initial plasma. Thehigh-density plasma is generated by applying a strong electric fieldacross the initial plasma as described herein. The RF power supplyapplies a negative voltage bias to the target assembly. Ions in thehigh-density plasma bombard the target material thereby causingsputtering.

[0108] A high-density plasma according to the present invention can beused to generate an ion beam. An ion beam source according to thepresent invention includes the plasma generating system 200 and anexternal electrode (not shown) that is used to accelerate ions in theplasma. In one embodiment, the external electrode is a grid. The ionbeam source can generate a very high-density ion flux. For example, theion beam source can generate ozone flux. Ozone is a highly reactiveoxidizing agent that can be used for many applications such as cleaningprocess chambers, deodorizing air, purifying water, and treatingindustrial wastes, for example.

[0109]FIG. 3 illustrates a cross-sectional view of a plasma generatingapparatus 300 including a magnet assembly 302 according to theinvention. The magnet assembly 302 can include permanent magnets 304, oralternatively, electro-magnets (not shown). In one embodiment, themagnet assembly 302 is adapted to create a magnetic field 306 proximateto the inner cathode section 202 a. The configuration of the magnetassembly 302 can be varied depending on the desired shape and strengthof the magnetic field 306. The magnet assembly 302 can have either abalanced or unbalanced configuration.

[0110] In one embodiment, the magnet assembly 302 includes switchingelectro-magnets, which generate a pulsed magnetic field proximate to theinner cathode section 202 a. In some embodiments, additional magnetassemblies (not shown) can be placed at various locations around andthroughout the process chamber (not shown).

[0111] The magnetic assembly 302 can be configured to generate amagnetic field in the shape of one or more racetracks (not shown).Magnetic fields in the shape of one or more racetracks can improvetarget utilization in sputtering targets by distributing regions ofhighest target erosion across the surface of the target. These regionsof high target erosion generally correspond to locations in which themagnetic field lines are parallel to the surface of the target.

[0112] In operation, the magnetic field 306 is generated proximate tothe inner cathode section 202 a. The permanent magnets 304 continuouslygenerate the magnetic field 306. Electro-magnets can also generate themagnetic field 306. The strength of the magnetic field 306 can be in therange of about fifty gauss to two thousand gauss. After the magneticfield 306 is generated, the feed gas 234 from the gas source 238 issupplied between the outer cathode section 202 b and the first anode210. A volume of the feed gas 234 fills in the region 214.

[0113] Next, the first power supply 206 generates an electric fieldacross the feed gas 234 to ignite an initial plasma in the region 214.The feed gas 234 flows through the region 214 and continuously displacesthe initial plasma. The initial plasma diffuses into the region 252′ andthe magnetic field 306 traps electrons in the initial plasma. A largefraction of the electrons are concentrated in the region 308 thatcorresponds to the weakest area of the magnetic field 306 that isgenerated by the magnet assembly 302. By trapping the electrons in theregion 308, the magnetic field 306, substantially prevents the initialplasma from diffusing away from the inner cathode section 202 a.

[0114] The second power supply 222 generates a strong electric fieldbetween the second anode 226 and the inner cathode section 202 a. Thestrong electric field super-ionizes the initial plasma to generate ahigh-density plasma having an ion density that is greater than the iondensity of the initial plasma. In one embodiment, the initial plasma hasan ion density that is in the range of about 10⁷ to 10¹² cm⁻³ and thehigh-density plasma has an ion density that is greater than about 10¹²cm⁻³.

[0115] The magnetic field 306 can improve the homogeneity of thehigh-density plasma. The magnetic field 306 can also increase the iondensity of the high-density plasma by trapping electrons in the initialplasma and also by trapping secondary electrons proximate to the innercathode section 202 a. The trapped electrons ionize excited atoms in theinitial plasma thereby generating the high-density plasma. In oneembodiment (not shown), a magnetic field is generated in the region 214that substantially traps electrons in the area where the initial plasmais ignited.

[0116] The magnetic field 306 also promotes increased homogeneity of thehigh-density plasma by setting up a substantially circular electron ExBdrift current 310 proximate to the inner cathode section 202 a. In oneembodiment, the electron ExB drift current 310 generates a magneticfield that interacts with the magnetic field 306 generated by the magnetassembly 302.

[0117] When high-power pulses are applied between the inner cathodesection 202 a and the second anode 226 secondary electrons are generatedfrom the inner cathode section 202 a that move in a substantiallycircular motion proximate to the inner cathode section 202 a accordingto crossed electric and magnetic fields. The substantially circularmotion of the electrons generates the electron ExB drift current 310.The magnitude of the electron ExB drift current 310 is proportional tothe magnitude of the discharge current in the plasma and, in oneembodiment, is approximately in the range of about three to ten timesthe magnitude of the discharge current.

[0118] In one embodiment, the substantially circular electron ExB driftcurrent 310 generates a magnetic field that interacts with the magneticfield 306 generated by the magnet assembly 302. In one embodiment, themagnetic field generated by the electron ExB drift current 310 has adirection that is substantially opposite to the magnetic field 306generated by the magnet assembly 302. The magnitude of the magneticfield generated by the electron ExB drift current 310 increases withincreased electron ExB drift current 310. The homogeneous diffusion ofthe high-density plasma in the region 252′ is caused, at least in part,by the interaction of the magnetic field 306 generated by the magnetassembly 302 and the magnetic field generated by the electron ExB driftcurrent 310.

[0119] In one embodiment, the electron ExB drift current 310 defines asubstantially circular shape for low current density plasma. However, asthe current density of the plasma increases, the substantially circularelectron ExB drift current 310 tends to have a more complex shape as theinteraction of the magnetic field 306 generated by the magnet assembly302, the electric field generated by the high-power pulse, and themagnetic field generated by the electron ExB drift current 310 becomesmore acute. For example, in one embodiment, the electron ExB driftcurrent 310 has a substantially cycloidal shape. The exact shape of theelectron ExB drift current 310 can be quite elaborate and depends onvarious factors.

[0120] As the magnitude of the electron ExB drift current 310 increases,the magnetic field generated by the electron ExB drift current 310becomes stronger and eventually overpowers the magnetic field 306generated by the magnet assembly 302. The magnetic field lines that aregenerated by the magnet assembly 302 exhibit substantial distortion thatis caused by the relatively strong magnetic field that is generated bythe relatively large electron ExB drift current 310. Thus, a largeelectron ExB drift current 310 generates a stronger magnetic field thatstrongly interacts with and can begin to dominate the magnetic field 306that is generated by the magnet assembly 302.

[0121] The interaction of the magnetic field 306 generated by the magnetassembly 302 and the magnetic field generated by the electron ExB driftcurrent 310 generates magnetic field lines that are somewhat moreparallel to the surface of the inner cathode section 202 a than themagnetic field lines generated by the magnet assembly 302. The somewhatmore parallel magnetic field lines allow the high-density plasma to moreuniformly distribute itself in the area 252′. Thus, the high-densityplasma is substantially uniformly diffused in the area 252′.

[0122]FIG. 4 illustrates a graphical representation 400 of applied poweras a function of time for periodic pulses applied to an initial plasmain the plasma generating system 200 of FIG. 2A. The first power supply206 generates a constant power and the second power supply 222 generatesperiodic power pulses. In one illustrative embodiment, the feed gas 234flows into the region 214 between the outer cathode section 202 b andthe first anode 210 at time t₀, before either the first power supply 206or the second power supply 222 are activated.

[0123] The time required for a sufficient quantity of feed gas 234 toflow into the region 214 depends on several factors including the flowrate of the feed gas 234 and the desired operating pressure. At time t₁,the first power supply 206 generates a power 402 that is in the range ofabout 0.01 kW to 100 kW and applies the power 402 between the outercathode section 202 b and the anode 210. The power 402 causes the feedgas 234 to become at least partially ionized, thereby generating aninitial plasma that can be a pre-ionization plasma as previouslydiscussed. An additional volume of feed gas flows into the region 214(FIG. 2A) between time t₁ and time t₂ substantially displacing theinitial plasma. The initial plasma is displaced into the region 252proximate to the inner cathode section 202 a.

[0124] At time t₂, the second power supply 222 delivers a high-powerpulse 404 to the initial plasma that is in the range of about 1 kW to 10MW depending on the volume and characteristics of the plasma and theoperating pressure. The high-power pulse 404 substantially super-ionizesthe initial plasma to generate a high-density plasma. The high-powerpulse 404 has a leading edge 406 having a rise time from t₂ to t₃ thatis approximately in the range of 0.1 microseconds to ten seconds. Inthis embodiment, the second power supply 222 is a pulsed power supply.In some embodiments (not shown), the second power supply 222 can be anRF power supply, an AC power supply, or a DC power supply.

[0125] In one embodiment, the pulse width of the high-power pulse 404 isin the range of about one microsecond to ten seconds. The high-powerpulse 404 is terminated at time t₄. In one embodiment, after thedelivery of the high-power pulse 404, the power 402 from the first powersupply 206 is continuously applied to generate additional plasma fromthe flowing feed gas 234, while the second power supply 222 prepares todeliver another high-power pulse 408.

[0126] At time t₅, the second power supply 222 delivers anotherhigh-power pulse 408 having a rise time from t₅ to t₆ and terminating attime t₇. In one embodiment, the repetition rate of the high-power pulsesis in the range of about 0.1 Hz to 10 kHz. The particular size, shape,width, and frequency of the high-power pulse 408 depend on the processparameters, such as the operating pressure, the design of the secondpower supply 222, the presence of a magnetic field proximate to theinner cathode section 202 a, and the volume and characteristics of theplasma, for example. The shape and duration of the leading edge 406 andthe trailing edge 410 of the high-power pulse 404 are chosen to controlthe rate of ionization of the high-density plasma.

[0127] In another embodiment (not shown), the first power supply 206and/or the second power supply 222 are activated at time t₀ before thefeed gas 234 flows in the region 214. In this embodiment, the feed gas234 is injected between the outer cathode section 202 b and the firstanode 210 where it is ignited by the first power supply 206 to generatethe initial plasma. In this embodiment, the first power supply 202 is aDC power supply. In other embodiments (not shown), the first powersupply 202 can an RF power supply, an AC power supply, or a pulsed powersupply.

[0128]FIG. 5 illustrates a cross-sectional view of a plasma generatingapparatus 500 including the magnet assembly 302 of FIG. 3 and anadditional magnet assembly 502 according to the invention. Theadditional magnet assembly 502 can include a permanent magnets 504 asshown, or alternatively, electro-magnets (not shown). In one embodiment,the magnet assembly 502 is adapted to create a magnetic field 506proximate to the outer cathode section 202 b. The configuration of themagnet assembly 502 can be varied depending on the desired shape andstrength of the magnetic field 506. The magnet assembly 502 can haveeither a balanced or unbalanced configuration.

[0129] In one embodiment, the magnet assembly 502 includes switchingelectro-magnets, which generate a pulsed magnetic field proximate to theouter cathode section 202 b. In some embodiments, additional magnetassemblies (not shown) can be placed at various locations around andthroughout the process chamber (not shown).

[0130] One skilled in the art will appreciate that there are many modesof operating the plasma generating apparatus 500. In one embodiment, theplasma generating apparatus 500 is operated by generating the magneticfield 506 proximate to the outer cathode section 202 b. In theembodiment shown in FIG. 5, the permanent magnets 504 continuouslygenerate the magnetic field 506. In other embodiments, electromagnets(not shown) generate the magnetic field 506 by energizing a currentsource (not shown) that is coupled to the electromagnets. In oneembodiment, the strength of the magnetic field 506 is in the range ofabout fifty gauss to two thousand gauss. After the magnetic field 506 isgenerated, the feed gas 234 from the gas source 238 is supplied betweenthe outer cathode section 202 b and the first anode 210. A volume of thefeed gas 234 fills in the region 214.

[0131] Next, the first power supply 206 generates an electric fieldacross the feed gas 234 to ignite an initial plasma in the region 214.In one embodiment, the magnetic field 506 substantially traps electronsin the initial plasma in the region 214. This causes the initial plasmato remain concentrated in the region 214. In one embodiment, the firstpower supply 206 applies a high-power pulse across the initial plasmathereby generating a high-density plasma in the region 214.

[0132] The high-power pulse energizes the electrons in the initialplasma. The magnetic field 506 causes the electrons to move in asubstantially circular manner creating a substantially circular electronExB drift current (not shown) proximate to the outer cathode section 202b. In one embodiment, the electron ExB drift current generates amagnetic field that interacts with the magnetic field 506 generated bythe magnet assembly 502.

[0133] The high-power pulses applied between the outer cathode section202 b and the first anode 210 generate secondary electrons from theouter cathode section 202 a that move in a substantially circular motionproximate to the inner cathode section 202 a according to crossedelectric and magnetic fields. The substantially circular motion of theelectrons generates the electron ExB drift current. The magnitude of theelectron ExB drift current is proportional to the magnitude of thedischarge current in the plasma and, in one embodiment, is approximatelyin the range of between about three and ten times the magnitude of thedischarge current. As previously discussed, the electron ExB driftcurrent can improve the homogeneity of the high-density plasma in theregion 214.

[0134]FIG. 6 illustrates a cross-sectional view of a plasma generatingapparatus 550 including the magnet assembly 302 of FIG. 3 and anadditional magnet assembly 552 according to the invention. Theadditional magnet assembly 552 can include permanent magnets 554, 556,or alternatively, electro-magnets (not shown). In one embodiment, themagnet assembly 552 is adapted to create a magnetic field 558 proximateto the outer cathode section 202 b. The configuration of the magnetassembly 552 can be varied depending on the desired shape and strengthof the magnetic field 558. The magnet assembly 552 can have either abalanced or unbalanced configuration.

[0135] The plasma generating apparatus 550 functions similarly to theplasma generating apparatus 500 of FIG. 5. However, the magneticassembly 552 that is located proximate to the outer cathode section 202b generates magnetic field lines 560 that are substantiallyperpendicular to a surface of the outer cathode section 202 b. Theperpendicular magnetic field lines 560 completely cross the region 214,thereby trapping substantially all of the electrons in the region 214.Thus, the magnetic field 558 can facilitate a more efficient process ofgenerating the initial plasma in the region 214. Skilled artisans willappreciate that alternative magnet configurations can be used within thescope of the invention.

[0136]FIG. 7 illustrates a cross-sectional view of another embodiment ofa plasma generating apparatus 600 including a magnet assembly 602according to the invention. The magnet assembly 602 can includepermanent magnets 604, or alternatively, electro-magnets (not shown). Inone embodiment, the magnet assembly 602 is adapted to create a magneticfield 606 that is located proximate to the inner cathode section 202 aand proximate to the outer cathode section 202 b. The configuration ofthe magnet assembly 602 can be varied depending on the desired shape andstrength of the magnetic field 606. The magnet assembly 602 can haveeither a balanced or unbalanced configuration.

[0137] In one embodiment, the magnet assembly 602 includes switchingelectro-magnets, which generate a pulsed magnetic field proximate to theinner 202 a and the outer cathode sections 202 b. In some embodiments,additional magnet assemblies (not shown) can be placed at variouslocations around and throughout the process chamber (not shown).

[0138] In one embodiment, the permanent magnets 604 continuouslygenerate the magnetic field 606. In other embodiments, electro-magnets(not shown) generate the magnetic field 606 by energizing a currentsource (not shown) that is coupled to the electro-magnets. In oneembodiment, the strength of the magnetic field 606 is in the range ofabout fifty gauss to two thousand gauss.

[0139] In operation, after the magnetic field 606 is generated, the feedgas 234 from the gas source 238 is supplied between the outer cathodesection 202 b and the first anode 210. A volume of the feed gas 234fills in the region 214.

[0140] Next, the first power supply 206 generates an electric fieldacross the feed gas 234 that ignites an initial plasma in the region214. In one embodiment, electrons in the initial plasma diffuse from theregion 214 to the region 608 substantially along magnetic field lines609 generated by the magnet assembly 602. In one embodiment, theelectrons in the initial plasma are concentrated in the region 608corresponding to the weakest area of the magnetic field 606 generated bythe magnet assembly 602. Thus, the initial plasma is concentratedproximate to the outer edge of the inner cathode section 202 a.

[0141] The second power supply 222 generates a strong electric fieldbetween the second anode 226 and the inner cathode section 202 a. Thestrong electric field super-ionizes the initial plasma to generate ahigh-density plasma having an ion density that is greater than the iondensity of the initial plasma. In one embodiment, the initial plasma hasan ion density in the of about 10⁷ to 10¹² cm⁻³. In one embodiment, thehigh-density plasma has an ion density that is greater than about 10¹²cm⁻³.

[0142] In one embodiment, the high-density plasma is used in a magnetronsputtering system (not shown). The magnetron sputtering system includesa target (not shown) that can be integrated into the inner cathodesection 202 a. Operating parameters can be chosen such that the outeredge of the target is eroded at a relatively high rate compared with thecenter of the target because the high-density plasma is concentrated inthe region 608. Thus, a sputtering system according to the presentinvention can include a target that is relatively small compared withknown sputtering systems for similarly sized substrates (not shown). Inaddition, the power level of the high-power pulse can be chosen suchthat the high-density plasma can be homogeneously distributed across thetarget as described herein.

[0143] The magnetic field 606 can improve the homogeneity of thehigh-density plasma and can increase the ion density of the high-densityplasma by trapping electrons in the initial plasma and also trappingsecondary electrons proximate to the target. The trapped electronsionize excited atoms in the initial plasma thereby generating thehigh-density plasma. The magnetic field 606 also promotes increasedhomogeneity of the high-density plasma by setting up an electron ExBdrift current 610 proximate to the target. In one embodiment, theelectron ExB drift current 610 generates a magnetic field that interactswith the magnetic field 606 generated by the magnet assembly 602 asdescribed herein.

[0144]FIG. 8 illustrates a cross-sectional view of a plasma generatingapparatus 650 including a magnet configuration that includes a firstmagnet 652 and a second magnet 654 according to the invention. The first652 and the second magnets 654 can be any type of magnet, such as apermanent ring-shaped magnet or an electro-magnet, for example.

[0145] The plasma generating apparatus 650 also includes a segmentedcathode 656. The segmented cathode 656 (656 a, b) includes an innercathode section 656 a and an outer cathode section 656 b. The outercathode section 656 b is disposed generally opposite to the innercathode section 656 a, but can be offset as shown in FIG. 8. Thesegmented cathode 656 illustrated in FIG. 8 can reduce sputteringcontamination compared with known cathodes used in sputtering systemsbecause both the inner cathode section 656 a and the outer cathodesection 656 b can include target material (not shown). Consequently, anymaterial that is sputtered from the outer cathode section 656 b istarget material instead of cathode material that could contaminate thesputtering process.

[0146] The plasma generating apparatus 650 also includes an anode 658.The anode 658 is disposed proximate to the inner cathode section 656 aand the outer cathode section 656 b. In one embodiment, the first output220 of the second power supply 222 is coupled to the inner cathodesection 656 a and the second output 224 of the second power supply 222is coupled to an input 660 of the anode 658.

[0147] In one embodiment, a first output 662 of a first power supply 664is coupled to the outer cathode section 656 b. A second output 666 ofthe first power supply 664 is coupled to the input 660 of the anode 658.In one embodiment (not shown), the anode 658 is coupled to groundpotential and the second output 224 of the second power supply 222 aswell as the second output 666 of the first power supply 664 are alsocoupled to ground potential.

[0148] The plasma generating apparatus 650 operates in a similar mannerto the plasma generating apparatus 200 of FIG. 2A. However, the magneticfield 668 generated by the first 652 and the second magnets 654 issubstantially parallel to at least a portion of the surface of the innercathode section 656 a. The shape of the magnetic field 668 can result ina homogeneous plasma volume that is located proximate to the innercathode section 656 a as discussed herein. Additionally, the magneticfield 668 traps substantially all of the secondary electrons from theinner-656 a and the outer cathode sections 656 b due to theconfiguration of the first 652 and the second magnets 654.

[0149] In one mode of operation, feed gas 234 from the gas source 238flows in the region 214 between the anode 658 and the outer cathodesection 656 b. In some embodiments, the feed gas source 240 suppliesfeed gas 236 between the inner cathode section 656 a and the anode 658.The first power supply 664 generates an electric field across the feedgas 234 that generates an initial plasma in the region 214. Electrons inthe initial plasma diffuse along the magnetic field lines of themagnetic field 668. Due to the configuration of the magnets 652 and 654,substantially all of the electrons in the initial plasma are trapped bythe magnetic field 668. The initial plasma diffuses towards the innercathode section 656 a as the feed gas 234 continues to flow.

[0150] After a suitable volume of the initial plasma is locatedproximate to the inner cathode section 656 a, the second power supply222 generates a strong electric field between the inner cathode section656 a and the anode 658. The strong electric field super-ionizes theinitial plasma and generates a high-density plasma having an ion densitythat is higher than the ion density of the initial plasma.

[0151]FIG. 9 illustrates a cross-sectional view of a plasma generatingapparatus 700 according to the present invention including a segmentedcathode assembly 702 (702 a, b), an ionizing electrode 708, and a first206, a second 222 and a third power supply 704. The first 206, thesecond 222, and the third power supplies 704 can each be any type ofpower supply suitable for plasma generation, such as a pulsed powersupply, a RF power supply, a DC power supply, or an AC power supply. Insome embodiments, the first 206, the second 222, and/or the third powersupplies 704 operate in a constant power or constant voltage mode asdescribed herein.

[0152] Only one portion of the segmented cathode assembly 702 is shownfor illustrative purposes. In one embodiment, the portion that is notshown in FIG. 9 is substantially symmetrical to the portion shown inFIG. 9. The plasma generating apparatus 700 also includes a first anode210 and a second anode 706. In one embodiment, the ionizing electrode708 is a filament-type electrode. The ionizing electrode 708 can bering-shaped or any other shape that is suitable for generating aninitial plasma in the region 214. Isolators 709 insulate the innercathode section 702 a from the outer cathode section 702 b. Theisolators 709 also insulate the second anode 706 from the inner 702 aand the outer cathode sections 702 b.

[0153] A first output 710 of the third power supply 704 is coupled tothe ionizing electrode 708. A second output 712 of the third powersupply 704 is coupled to the outer cathode section 702 b. The powergenerated by the third power supply 704 is sufficient to ignite a feedgas 234 located in the region 214 to generate an initial plasma.

[0154] The first output 204 of the first power supply 206 is coupled tothe outer cathode section 702 b. The second output 208 of the firstpower supply 206 is coupled to the first anode 210. The power generatedby the first power supply 206 is sufficient to increase the ion densityof the initial plasma in the region 214.

[0155] The first output 220 of the second power supply 222 is coupled tothe inner cathode section 702 a. The second output 224 of the secondpower supply 222 is coupled to the second anode 706.

[0156] In operation, the first power supply 206 is a pulsed power supplythat applies a high-power pulse between the outer cathode section 702 band the first anode 210. The high-power pulse generates an electricfield (not shown) through the region 214. The electric field generates ahigh-density plasma from the initial plasma that is generated by theionizing electrode 708. The high-density plasma is generally morestrongly ionized than the initial plasma.

[0157] In one embodiment, the feed gas 234 continues to flow after thehigh-density plasma is generated in the region 214. The feed gas 234displaces the high-density plasma towards the inner cathode region 702a. The feed gas exchange continues until a suitable volume of thehigh-density plasma is located proximate to the inner cathode section702 a.

[0158] In one embodiment, the second power supply 222 is a pulsed powersupply that applies a high-power pulse across the high-density plasma.The high-power pulse generates an electric field (not shown) between theinner cathode section 702 a and the second anode 706. The electric fieldgenerates a plasma that is generally more strongly-ionized than thehigh-density plasma.

[0159] The plasma generating apparatus 700 of the present inventiongenerates a very high-density plasma using standard power supplies. Theplasma generating apparatus 700 of the present invention can generate avery high-density plasma at a lower cost compared with a known plasmagenerating apparatus because the plasma generating apparatus 700 can userelatively inexpensive and commercially available power supplies. Inplasma sputtering applications, the sputtering targets that are used inthe plasma generating apparatus 700 can be much smaller relative tocomparable sputtering targets that are used in known magnetronsputtering systems used to process similarly sized substrates.

[0160]FIG. 10 illustrates a cross-sectional view of a plasma generatingapparatus 720 according to the present invention including a segmentedcathode assembly 722 (722 a, b), a common anode 724, an ionizingelectrode 708, and a first 206, a second 222, and a third power supply704. The first 206, the second 222, and the third power supplies 704 caneach be any type of power supply suitable for plasma generation, such asa pulsed power supply, a RF power supply, a DC power supply, or an ACpower supply. In some embodiments, the first 206, the second 222, and/orthe third power supplies 704 operate in a constant power or constantvoltage mode as described herein.

[0161] Only one portion of the segmented cathode assembly 722 is shownfor illustrative purposes. In one embodiment, the portion that is notshown in FIG. 10 is substantially symmetrical to the portion shown inFIG. 10. In one embodiment, the ionizing electrode 708 is afilament-type electrode. The ionizing electrode 708 can be ring-shapedor any other shape that is suitable for generating an initial plasma inthe region 214. An isolator 726 insulates the anode 724 from the innercathode section 722 a. An isolator 728 insulates the anode 724 from theouter cathode section 722 b.

[0162] In a plasma sputtering configuration, the segmented cathodeassembly 722 illustrated in FIG. 10 can reduce sputtering contaminationcompared with known cathodes used in sputtering systems because both theinner cathode section 722 a and the outer cathode section 722 b caninclude target material (not shown). Consequently, any material that issputtered from the outer cathode section 722 b is target materialinstead of cathode material that could contaminate the sputteringprocess.

[0163] A first output 710 of the third power supply 704 is coupled tothe ionizing electrode 708. A second output 712 of the third powersupply 704 is coupled to the outer cathode section 722 b. The powergenerated by the third power supply 704 is sufficient to ignite a feedgas 234 located in the region 214 to generate an initial plasma.

[0164] The first output 204 of the first power supply 206 is coupled tothe anode 724. The second output 208 of the first power supply 206 iscoupled to the outer cathode, section 722 b. The power generated by thefirst power supply 206 is sufficient to increase the ion density of theinitial plasma in the region 214.

[0165] The first output 220 of the second power supply 222 is coupled tothe inner cathode section 722 a. The second output 224 of the secondpower supply 222 is coupled to the anode 724.

[0166] In operation, the first power supply 206 is a pulsed power supplythat applies a high-power pulse between the outer cathode section 722 band the anode 724. The high-power pulse generates an electric fieldthrough the region 214. The electric field generates a high-densityplasma from the initial plasma. The high-density plasma is generallymore strongly ionized than the initial plasma.

[0167] In one embodiment, the feed gas 234 continues to flow after thehigh-density plasma is generated in the region 214. The feed gas 234displaces the high-density plasma towards the inner cathode region 722a. The feed gas exchange continues until a suitable volume of thehigh-density plasma is located proximate to the inner cathode section722 a.

[0168] In one embodiment, the second power supply 222 is a pulsed powersupply that applies a high-power pulse across the high-density plasma.The high-power pulse generates a strong electric field between the innercathode section 722 a and the anode 724. The strong electric fieldgenerates a plasma that is generally more strongly-ionized than thehigh-density plasma.

[0169]FIG. 11 illustrates a cross-sectional view of a plasma generatingapparatus 725 according to the present invention including the segmentedcathode assembly 702 (702 a, b) and a first 206, a second 222 and athird power supply 704. The first 206, the second 222, and the thirdpower supplies 704 can each be any type of power supply suitable forplasma generation, such as a pulsed power supply, a RF power supply, aDC power supply, or an AC power supply. In some embodiments, the first206, the second 222, and/or the third power supplies 704 operate in aconstant power or constant voltage mode as described herein. The first206 and the third power supplies 704 can be integrated into a singlepower supply.

[0170] Only one portion of the segmented cathode assembly 702 is shownfor illustrative purposes. In one embodiment, the portion that is notshown in FIG. 11 is substantially symmetrical to the portion shown inFIG. 11. The plasma generating apparatus 725 also includes a first anode210 and a second anode 706. Isolators 709 insulate the inner cathodesection 702 a from the outer cathode section 702 b and insulate thesecond anode 706 from the inner 702 a and the outer cathode sections 702b.

[0171] A first output 710 of the third power supply 704 is coupled tothe outer cathode section 702 b. A second output 712 of the third powersupply 704 is coupled to the first anode 210. The power generated by thethird power supply 704 is sufficient to ignite a feed gas 234 located inthe region 214 to generate an initial plasma.

[0172] A first output 204 of the first power supply 206 is coupled tothe outer cathode section 702 b. A second output 208 of the first powersupply 206 is coupled to the first anode 210. A first output 220 of thesecond power supply 222 is coupled to the inner cathode section 702 a. Asecond output 224 of the second power supply 222 is coupled to thesecond anode 706.

[0173] In operation, the power generated by the first power supply 206is sufficient to increase the ion density of the initial plasma in theregion 214 that is generated by the third power supply 704. In oneembodiment, the first power supply 206 is a pulsed power supply thatapplies a high-power pulse between the outer cathode section 702 b andthe first anode 210. The high-power pulse generates an electric fieldthrough the region 214. The electric field generates a high-densityplasma from the initial plasma. The high-density plasma is generallymore strongly ionized than the initial plasma.

[0174] In one embodiment, the feed gas 234 continues to flow after thehigh-density plasma is generated in the region 214. The feed gas 234displaces the high-density plasma towards the inner cathode region 702a. The feed gas exchange continues until a suitable volume of thehigh-density plasma is located proximate to the inner cathode section702 a.

[0175] In one embodiment, the second power supply 222 is a pulsed powersupply that applies a high-power pulse across the high-density plasma.The high-power pulse generates a strong electric field between the innercathode section 702 a and the second anode 706. The strong electricfield generates a plasma that is generally more strongly-ionized thanthe high-density plasma.

[0176] The plasma generating apparatus 725 of the present inventiongenerates a very high-density plasma using standard power supplies. Theplasma generating apparatus 725 of the present invention can generate avery high-density plasma at a lower cost compared with a known plasmagenerating apparatus because the plasma generating apparatus 725 can userelatively inexpensive and commercially available power supplies.

[0177] There are many modes of operation for the plasma generatingapparatus 725. For example, the first power supply 206 and the secondpower supply 222 can both be operated in constant power mode. In anothermode of operation, the first power supply 206 is operated in constantpower mode and the second power supply 222 is operated in constantvoltage mode. In still another mode of operation, the first 206 and thesecond power supplies 222 are both operated in constant voltage mode.Some of these modes of operation are discussed in more detail herein.

[0178]FIG. 12 illustrates a cross-sectional view of a plasma generatingapparatus 730 according to the present invention including a segmentedcathode assembly 732 (732 a, b), a second anode 706, a first 731 and asecond power supply 222. In this embodiment, the outer cathode sectionis in the form of an excited atom source 732 b. The excited atom source732 b generates excited atoms including metastable atoms from groundstate atoms in the feed gas 234. In another embodiment (not shown), theouter cathode section 732 b is in the form of a hollow cathode. Skilledartisans will appreciate that multiple excited atom sources (not shown)can surround the inner cathode section 732 a.

[0179] The first 731 and the second power supplies 222 can be any typeof power supplies suitable for plasma generation, such as pulsed powersupplies, RF power supplies, DC power supplies, or AC power supplies. Insome embodiments, the first 731 and/or the second power supplies 222operate in a constant power or constant voltage mode as describedherein.

[0180] Only one portion of the segmented cathode assembly 732 is shownfor illustrative purposes. In one embodiment, the portion that is notshown is substantially symmetrical to the portion shown in FIG. 12. Theinner cathode section 732 a can be electrically isolated from theexcited atom source 732 b. Isolators 709 insulate the second anode 706from the inner cathode section 732 a and the excited atom source 732 b.

[0181] The excited atom source 732 b includes a tube 733. The tube 733can be formed of non-conducting material, such as a dielectric material,like boron nitride or quartz, for example. A nozzle 734 is positioned atone end of the tube 733. The nozzle 734 can be formed from a ceramicmaterial. The tube 733 is surrounded by an enclosure 735. A skimmer 736having an aperture 737 is positioned adjacent to the nozzle 734 forminga nozzle chamber 738. The skimmer 736 can be connected to the enclosure735. In one embodiment, the skimmer 736 is cone-shaped as shown in FIG.12. In one embodiment, the enclosure 735 and the skimmer 736 areelectrically connected to ground potential.

[0182] The tube 733 and the enclosure 735 define an electrode chamber739 that is in fluid communication with a gas inlet 740. A feed gassource (not shown) is coupled to the gas inlet 740 so as to allow feedgas 234 to flow into the electrode chamber 739. An electrode 741 ispositioned inside the electrode chamber 739 adjacent to the nozzle 734and to the skimmer 736. In one embodiment, the electrode 741 is a needleelectrode, as shown in FIG. 12. The needle electrode generates arelatively high electric field at the tip of the electrode. Theelectrode 741 is electrically isolated from the skimmer 736.

[0183] A first output 742 of the first power supply 731 is coupled tothe needle electrode 741 with a transmission line 743. An insulator 744isolates the transmission line 743 from the grounded enclosure 735. Asecond output 745 of the first power supply 737 is coupled to ground.

[0184] A first output 220 of the second power supply 222 is coupled tothe inner cathode section 732 a. A second output 224 of the second powersupply 222 is coupled to the second anode 706. In one embodiment, thesecond power supply 222 generates an electric field between the innercathode section 732 a and the second anode 706.

[0185] The plasma generating apparatus 730 of the present inventiongenerates a high-density plasma using standard power supplies. Theplasma generating apparatus 730 of the present invention can generate ahigh-density plasma at a lower cost compared with known plasmagenerating apparatus because the plasma generating apparatus 730 can userelatively inexpensive and commercially available power supplies. Inaddition, the sputtering targets that can be used in the plasmagenerating apparatus 730 can be much smaller relative to comparablesputtering targets that are used in known magnetron sputtering systemsused to process similarly sized substrates.

[0186] There are many modes of operation for the plasma generatingapparatus 730. For example, the first power supply 731 and the secondpower supply 222 can both be operated in constant power mode. In anothermode of operation, the first power supply 731 is operated in constantpower mode and the second power supply 222 is operated in constantvoltage mode. In still another mode of operation, the first 731 and thesecond power supplies 222 are both operated in constant voltage mode.Some of these modes of operation are discussed in more detail herein.

[0187] In one illustrative mode of operation, ground state atoms in thefeed gas 234 are supplied to the excited atom source 732 b through thegas inlet 740. The pressure in the electrode chamber 739 is optimized toproduce exited atoms including metastable atoms by adjusting parameters,such as the flow rate of the feed gas 234, the diameter of the nozzle734, and the diameter of the aperture 737 of the skimmer 736. The firstpower supply 731 generates an electric field (not shown) between theneedle electrode 741 and the skimmer 736. The electric field raises theenergy of the ground state atoms to an excited state that generatesexcited atoms. Many of the excited atoms are metastable atoms. Theelectric field can also generate some ions and electrons along with theexited atoms.

[0188] Optional magnets 746 generate a magnetic field 747 proximate tothe excited atom source 732 b. The magnetic field 747 can be used toassist in exciting the ground state atoms. The magnetic field 747 trapsaccelerated electrons proximate to the electric field. Some of theaccelerated electrons impact a portion of the ground state atoms,thereby transferring energy to those ground state atoms. This energytransfer excites at least a portion of the ground state atoms to createa volume of excited atoms including metastable atoms.

[0189] A portion of the volume of excited atoms as well as some ions,electrons and ground state atoms flow through the nozzle 734 into thenozzle chamber 738 as additional feed gas flows into the electrodechamber 739. A large fraction of the ions and electrons are trapped inthe nozzle chamber 738 while the excited atoms and the ground stateatoms flow through the aperture 737 of the skimmer 736.

[0190] After a sufficient volume of excited atoms including metastableatoms is present proximate to the inner cathode section 732 a, thesecond power supply 222 generates an electric field (not shown)proximate to the volume of excited atoms between the inner cathodesection 732 a and the second anode 706. The electric field raises theenergy of the volume of excited atoms causing collisions between neutralatoms, electrons, and excited atoms including metastable atoms. Thesecollisions generate the plasma proximate to the inner cathode section732 a. The plasma includes ions, excited atoms and additional metastableatoms. The efficiency of this multi-step ionization process increases asthe density of excited atom and metastable atoms increases.

[0191] In one embodiment, a magnetic field is generated proximate to theinner cathode section 732 a. The magnetic field can increase the iondensity of the plasma by trapping electrons in the plasma and also bytrapping secondary electrons proximate to the inner cathode section 732a.

[0192] All noble gas atoms have metastable states. For example, argonmetastable atoms can be generated by a multi-step ionization process. Ina first step, ionizing electrons e⁻ are generated by applying asufficient voltage across argon feed gas containing ground state argonatoms. When an ionizing electron e⁻ collides with a ground state argon(Ar) atom, a metastable argon atom and an electron are generated. Argonhas two metastable states, see Fabrikant, 1.1., Shpenik, O. B.,Snegursky, A. V., and Zavilopulo, A. N., Electron Impact Formation ofMetastable Atoms, North-Holland, Amsterdam. In a second step in themulti-step ionization process, the metastable argon atom is ionized.

[0193] The multi-step ionization process described herein substantiallyincreases the rate at which the plasma is formed and, therefore,generates a relatively dense plasma. The rate is increased because onlya relatively small amount of energy is required to ionize the metastableatoms as described herein. For example, ground state argon atoms requireenergy of about 15.76 eV to ionize. However, argon metastable atomsrequire only about 4 eV of energy to ionize. The excited atom source 732b provides the energies of about 11.55 eV and 11.72 eV that arenecessary to reach argon metastable states. Therefore, a volume ofmetastable atoms will ionize at a much higher rate than a similar volumeof ground state atoms for the same input energy.

[0194] Furthermore, as the density of the metastable atoms in the plasmaincreases, the efficiency of the ionization process rapidly increases.The increased efficiency results in an avalanche-like process thatsubstantially increases the density of the plasma. In addition, the ionsin the plasma strike the inner cathode section 732 a causing secondaryelectron emission from the inner cathode section 732 a. The secondaryelectrons interact with ground state atoms and with the excited atomsincluding the metastable atoms in the plasma. This interaction furtherincreases the density of ions in the plasma as additional volumes ofmetastable atoms become available. Thus, for the same input energy, thedensity of the plasma that is generated by the multi-step ionizationprocess according to the present invention is significantly greater thana plasma that is generated by direct ionization of ground state atoms.

[0195]FIG. 13 illustrates a graphical representation 750 of power as afunction of time for each of a first 206, a second 222, and a thirdpower supply 704 for one mode of operating the plasma generating system700 of FIG. 9. The first 206, second 222, and third power supplies 704are synchronized to each other to optimize certain properties of theplasma. For example, the third power supply 704 generates a constantpower throughout the process, while the first 206 and the second powersupplies 222 generate periodic power pulses at preset intervals.Although FIG. 13 relates to the operation of FIG. 9, skilled artisanswill appreciate that the plasma generating systems 720, 725 of FIG. 10and FIG. 11, respectively, can be operated in a similar manner to theplasma generating system 700 of FIG. 9. In one mode of operation, thefirst power supply 206 and the second power supply 222 are operated in aconstant power mode.

[0196] In this mode, the plasma generating apparatus 700 can operate asfollows. At time t₀, the third power supply 704 applies a constant power752 in the range of about 0.1 kW to 10 kW across the feed gas 234 togenerate an initial plasma. The power level required to generate theinitial plasma depends on several factors including the dimensions ofthe region 214, for example. The constant power 752 is applied betweenthe ionizing electrode 708 and the outer cathode section 702 b. Theinitial plasma diffuses towards the inner cathode section 702 a due to apressure differential as described herein. The pressure differentialconcentrates the initial plasma from the region 214 towards the innercathode section 702 a.

[0197] At time t₁, the second power supply 222 applies a constant power754 in the range of about 0.1 kW to 10 kW across the initial plasma toincrease the ion density of the initial plasma and to sustain theinitial plasma proximate to the inner cathode section 702 a. The timeperiod between time t₀ and time t₁ is in the range of about 0.1 msec to1 sec and depends on several parameters including the dimensions of theinner cathode section 702 a, for example.

[0198] At time t₂, a sufficient volume of the initial plasma is locatedproximate to the inner cathode section 702 a and an additional volume ofinitial plasma is generated in the region 214. The first power supply206 then applies a high power pulse 756 across the additional volume ofinitial plasma in the region 214 to generate a high-density plasma inthe region 214. The ion density of the high-density plasma is greaterthan the ion density of the initial plasma. The high-power pulse 756 hasa power level that is in the range of about 10 kW to 1,000 kW. The timeperiod between time t₁ and time t₂ is in the range of about 0.1 msec to1 sec.

[0199] The high-density plasma that is generated in the region 214diffuses toward the inner cathode section 702 a due to the pressuredifferential. At time t₃, the second power supply 222 applies ahigh-power pulse 758 to the high-density plasma in order to super-ionizethe high-density plasma to further increase the plasma density. The timeperiod between time t₂ and time t₃ is in the range of about 0.001 msecto 1 msec. The time period of the high-power pulse 758 between time t₃and time t₄ is in the range of about 0.1 msec to 10 sec.

[0200] Additionally, between time t₃ and time t₅, the first power supply206 continues to apply the high-power pulse 756 in order to sustain thehigh-density plasma. At time t₅, the high-power pulse 756 terminates.The second power supply 222 continues to apply a background power 760after the high-power pulse 758 terminates at time t₄. The backgroundpower 760 continues to sustain the high-density plasma. The time periodbetween time t₄ and time t₅ is in the range of about 0.001 msec to 1msec.

[0201] At time t₅, the high power pulse 756 generated by the first powersupply 206 terminates. At time t₆, the first power supply 206 appliesanother high-power pulse 762 across a new volume of high-density plasmain the region 214. The high-power pulse 762 increases the currentdensity in the new volume of high-density plasma. The new volume ofhigh-density plasma diffuses towards the inner cathode section 702 a. Attime t₇, the second power supply 222 applies another high-power pulse764 to the new volume of high-density plasma that is located proximateto the inner cathode section 702 a. At time t₈, the high-power pulse 764terminates. At time t₉, the high power pulse 762 from the first powersupply 206 terminates.

[0202] The power from the third power supply 704 is continuously appliedfor a time that is in the range of about one microsecond to one hundredseconds in order to allow the initial plasma to form and to bemaintained at a sufficient plasma density. The power from the secondpower supply 222 can be continuously applied after the initial plasma isignited in order to maintain the initial plasma. The second power supply222 can be designed so as to output a continuous nominal power in orderto generate and sustain the initial plasma until a high-power pulse isdelivered by the second power supply 222. The high-power pulse has aleading edge having a rise time that is in the range of about 0.1microseconds to ten seconds.

[0203] The high-power pulse 756 has a power and a pulse width that issufficient to transform the initial plasma to a strongly-ionizedhigh-density plasma. The high-power pulse 756 is applied for a time thatis in the range of about ten microseconds to ten seconds. The repetitionrate of the high-power pulses 756, 762 is in the range of about 0.1 Hzto 1 kHz.

[0204] The particular size, shape, width, and frequency of thehigh-power pulses 756, 762 depend on various factors including processparameters, the design of the first power supply 206, the design of theplasma generating apparatus 700, the volume of the plasma, and thepressure in the chamber. The shape and duration of the leading edge andthe trailing edge of the high-power pulse 756 is chosen to sustain theinitial plasma while controlling the rate of ionization of thehigh-density plasma.

[0205]FIG. 14 illustrates a graphical representation 770 of powergenerated as a function of time for each of a first 206, a second 222,and a third power supply 704 for one mode of operating the plasmagenerating system 700 of FIG. 9. The plasma generating apparatus 700 hasmany operating modes. For example, in this mode, the first power supply206 is operated in voltage mode, while the second power supply can beoperated in power mode.

[0206] In this mode, the plasma generating apparatus 700 can operate asfollows. At time t₀, the third power supply 704 applies a constant power772 in the range of about 0.1 kW to 10 kW across the feed gas 234 togenerate an initial plasma. In one embodiment, the power from the thirdpower supply 704 is continuously applied for a time that is in the rangeof about one microsecond to one hundred seconds in order to allow theinitial plasma to form and to be maintained at a sufficient plasmadensity.

[0207] The initial plasma diffuses towards the inner cathode section 702a. At time t₁, the second power supply 222 applies a constant power 774in the range of about 0.1 kW to 10 kW across the initial plasma toincrease the ion density of the initial plasma and to maintain/sustainthe initial plasma proximate to the inner cathode section 702 a.

[0208] A pressure differential forces the initial plasma from the region214 towards the inner cathode region 702 a. At time t₂, the first powersupply 206 applies a ramping power pulse 776 across the initial plasmain the region 214 in order to generate a high-density plasma in theregion 214. The ramping power pulse 776 has a power and a rise time thatis sufficient to transform the initial plasma to a strongly-ionizedhigh-density plasma.

[0209] The ramping power pulse 776 has a power that is in the range ofabout 10 kW to 1,000 kW and the ramping power pulse 776 is applied for atime that is in the range of between about ten microseconds to tenseconds. The repetition rate between the ramping power pulses 776 isbetween about 0.1 Hz and 1 kHz. The shape and duration of the leadingedge and the trailing edge of the ramping power pulse 776 is chosen tosustain the initial plasma while controlling the rate of ionization ofthe high-density plasma. The high-density plasma diffuses toward theinner cathode section 702 a.

[0210] At time t₃, the second power supply 222 applies a high-powerpulse 778 to the high-density plasma to generate a higher-densityplasma. At time t₄, the high-power pulse and the ramping power pulse 776terminate. The second power supply 222 continues to apply a backgroundpower 780 to sustain the plasma after the high-power pulse 778terminates. The second power supply 222 can be designed so as togenerate a continuous nominal power that generates and sustains theinitial plasma until a high-power pulse is delivered by the second powersupply 222. In one embodiment, the high-power pulse has a leading edgewith a rise time that is in the range of about 0.1 microseconds to tenseconds.

[0211] At time t₅, the first power supply 206 applies another rampingpower pulse 782 across an additional volume of initial plasma in theregion 214. The ramping power pulse 782 increases the current density inthe additional volume of initial plasma to generate a high-densityplasma. At time t₆, the second power supply 222 applies anotherhigh-power pulse 784 to the high-density plasma that is locatedproximate to the inner cathode section 702 a. The high-power pulsegenerates a higher density plasma proximate to the inner cathode section702 a. At time t₇, the high-power pulse 784 and the ramping power pulse782 terminate. In one embodiment, the repetition rate between theramping power pulses 776, 782 is between about 0.1 Hz and 1 kHz.

[0212]FIG. 15 illustrates a graphical representation 790 of power as afunction of time for each of a first 206, a second 222, and a thirdpower supply 704 for one mode of operating the plasma generating system700 of FIG. 9. In this mode, the second power supply 222 is a RF powersupply. A RF power supply can be used in plasma sputtering systems forsputtering magnetic materials or dielectric materials, for example. Inthis mode of operation, the first power supply 206 is operated in aconstant power mode. Due to the nature of a RF power supply, the secondpower supply 222 is operated in a substantially constant power mode.

[0213] In this mode, the plasma generating apparatus 700 can operate asfollows. At time t₀, the third power supply 704 applies a constant power752 in the range of about 0.1 kW to 10 kW across the feed gas 234 togenerate an initial plasma. The power level required to generate theinitial plasma depends on several factors including the dimensions ofthe region 214, for example. The constant power 752 is applied betweenthe ionizing electrode 708 and the outer cathode section 702 b. Theinitial plasma diffuses towards the inner cathode section 702 a due to apressure differential as described herein. The pressure differentialforces the initial plasma from the region 214 towards the inner cathodesection 702 a.

[0214] At time t₁, the second power supply 222 applies an RF drivingvoltage corresponding to a power 792 in the range of about 0.1 kW to 10kW across the initial plasma to sustain the initial plasma proximate tothe inner cathode section 702 a. The RF power supply generates a seriesof very short sinusoidal voltage pulses having a time period betweentime t₀ and time t₁ that is in the range of about 0.1 msec to 1 sec andthat depends on several parameters, such as the dimensions of the innercathode section 702 a.

[0215] At time t₂, a sufficient volume of the initial plasma is locatedproximate to the inner cathode section 702 a and an additional volume ofinitial plasma is generated in the region 214. The first power supply206 then applies a high-power pulse 756 across the additional volume ofinitial plasma in the region 214 to generate a high-density plasma inthe region 214. The ion density of the high-density plasma is greaterthan the ion density of the initial plasma. The high-power pulse 756 hasa power level that is in the range of about 10 kW to 1,000 kW. In oneembodiment, the time period between time t₁ and time t₂ is in the rangeof about 0.1 msec to 1 sec.

[0216] The high-density plasma that is generated in the region 214diffuses toward the inner cathode section 702 a due to the pressuredifferential. At time t₃, the second power supply 222 applies ahigh-power RF pulse 794 to the high-density plasma. The high-power RFpulse super-ionizes the high-density plasma, thereby generating ahigher-density plasma. In one embodiment, the frequency of thehigh-power pulse 794 is 13.56 MHz. In other embodiments, the frequencyof the high power RF pulse 794 is in the range of about 40 kHz to 100MHz.

[0217] In one embodiment, the time period between time t₂ and time t₃ isin the range of about 0.001 msec to 1 msec. The total time period of thehigh-power pulse 794 between time t₃ and time t₄ is in the range ofabout 0.01 microsec to 10 sec.

[0218] Additionally, between time t₃ and time t₅, the first power supply206 continues to apply the high-power pulse 756 in order to maintain thehigh-density plasma. At time t₅, the high-power pulse 756 terminates. Inone embodiment, the second power supply 222 continues to apply abackground RF driving voltage corresponding to a power 796 after thehigh-power pulse 794 terminates at time t₄. The background RF power 796continues to maintain the high-density plasma. The time period betweentime t₄ and time t₅ is in the range of about 0.001 msec to 1 msec.

[0219] At time t₆, the first power supply 206 applies another high-powerpulse 762 across a new volume of initial plasma in the region 214. Thehigh-power pulse 762 generates a new volume of high-density plasma. Thenew volume of high-density plasma diffuses towards the inner cathodesection 702 a. At time t₇, the second power supply 222 applies RFdriving voltage corresponding to another high-power pulse 798 to the newvolume of high-density plasma that is located proximate to the innercathode section 702 a. At time t₈, the high-power pulse 798 terminates.At time t₉, the high power pulse 762 from the first power supply 206terminates.

[0220] The power 752 from the third power supply 704 is continuouslyapplied for a time that is in the range of about one microsecond to onehundred seconds in order to allow the initial plasma to form and to bemaintained at a sufficient plasma density. In one embodiment, the RFpower from the second power supply 222 is continuously applied after theinitial plasma is ignited in order to maintain the initial plasma.

[0221] The high-power pulse 756 has a power and a pulse width that issufficient to transform the initial plasma to a strongly-ionizedhigh-density plasma. The high-power pulse 756 is applied for a time thatis in the range of about ten microseconds to ten seconds. The repetitionrate of the high-power pulses 756, 762 is in the range of about 0.1 Hzto 1 kHz.

[0222] The particular size, shape, width, and frequency of thehigh-power pulses 756, 762 depend on various factors including processparameters, the design of the first power supply 206, the design of theplasma generating apparatus 700, the volume of the plasma, and thepressure in the chamber, for example. The shape and duration of theleading edge and the trailing edge of the high-power pulse 756 is chosento sustain the initial plasma while controlling the rate of ionizationof the high-density plasma.

[0223]FIG. 16A through FIG. 16C are flowcharts 800, 800′, and 800″ ofillustrative processes of generating high-density plasmas according tothe present invention. Referring to FIG. 16A, the feed gas 234 (FIG. 2)flows into the region 214 (step 802). The feed gas 234 flows through theregion 214 towards the inner cathode section 202 a. Next, the firstpower supply 206 generates a voltage across the feed gas 234 in theregion 214 (step 804). The voltage generates an electric field that islarge enough to ignite the feed gas 234 and generate the initial plasma.While the initial plasma is being generated, additional feed gas flowsinto the region 214 forcing the initial plasma to diffuse proximate tothe inner cathode section 202 a (step 806).

[0224] After a suitable volume of the initial plasma is present in theregion 252, the second power supply 222 generates a large electric fieldacross the initial plasma that super-ionizes the initial plasma, therebygenerating a high-density plasma in the region 252 (step 808). Thehigh-density plasma is typically more strongly ionized than the initialplasma.

[0225] In the process illustrated in FIG. 16B, the feed gas 234 flowsinto the region 214 (step 802). In one embodiment, the feed gas 234flows through the region 214 towards the inner cathode section 202 a.Next, the first power supply 206 generates a voltage across the feed gas234 in the region 214 (step 804). The voltage is large enough to ignitethe feed gas 234 and to generate the initial plasma. While the initialplasma is being generated, additional feed gas 234 flows into the region214 forcing the initial plasma to diffuse proximate to the inner cathodesection 202 a (step 806).

[0226] Once the initial plasma is generated in the region 214, the firstpower supply 206 generates a strong electric field across the initialplasma, thereby super-ionizing the initial plasma and creating ahigh-density plasma in the region 214 (step 810). In one embodiment, anadditional power supply (not shown) generates the strong electric fieldinstead of the first power supply 206.

[0227] The high-density plasma diffuses towards the inner cathodesection 202 a where it commingles with the initial plasma in the region252 (step 812). When a suitable volume of the combined plasma is presentin the region 252, the second power supply 222 generates a strongelectric field across the plasma in the region 252 that generates ahigh-density plasma (step 814). The high-density plasma will typicallybe more strongly-ionized than the plasma formed from the combination ofthe initial plasma and the high-density plasma from the region 214.

[0228] In the embodiment illustrated in FIG. 16C, the feed gas 234 flowsinto the region 214 (step 816). In one embodiment, the feed gas 234flows through the region 214 towards the inner cathode section 202 a.Next, the first power supply 206 generates a voltage across the feed gas234 in the region 214 (step 818). The voltage generates an electricfield that is large enough to ignite the feed gas 234 and generate theinitial plasma. In this embodiment, additional feed gas 234 is notsupplied to the region 214 and therefore, the initial plasma remains inthe region 214.

[0229] Once the initial plasma is generated in the region 214, the firstpower supply 206 generates a strong electric field across the initialplasma, thereby super-ionizing the initial plasma and creating ahigh-density plasma in the region 214 (step 820). In one embodiment, anadditional power supply (not shown) generates the strong electric fieldinstead of the first power supply 206. Once the high-density plasma ispresent in the region 214, additional feed gas 234 is supplied to theregion 214, displacing the high-density plasma towards the inner cathodesection 202 a (step 822).

[0230] When a suitable volume of high-density plasma is present in theregion 252, the second power supply 222 generates a strong electricfield across the high-density plasma in the region 252 to generate ahigher-density plasma (step 824). The higher-density plasma willtypically be more strongly-ionized than the high-density plasma from theregion 214.

[0231] While the invention has been particularly shown and describedwith reference to specific preferred embodiments, it should beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention as defined herein.

What is claimed is:
 1. A plasma source comprising: a cathode assemblycomprising an inner cathode section and an outer cathode section; ananode that is positioned adjacent to the outer cathode section andforming a gap there between; a first power supply that generates a firstelectric field across the gap, the first electric field ionizing avolume of feed gas that is located in the gap, thereby generating aninitial plasma; and a second power supply that generates a secondelectric field proximate to the inner cathode section, the secondelectric field super-ionizing the initial plasma to generate a plasmacomprising a higher density of ions than the initial plasma.
 2. Theplasma source of claim 1 further comprising a second anode that ispositioned adjacent to the inner cathode section, the second powersupply generating the second electric field between the inner cathodesection and the second anode.
 3. The plasma source of claim 1 whereinthe first and the second power supplies are chosen from the groupcomprising a pulsed DC power supply, an AC power supply, a DC powersupply, and a RF power supply.
 4. The plasma source of claim 1 whereinthe first power supply further generates a third electric field acrossthe gap, the third electric field super-ionizing the initial plasma thatis located in the gap.
 5. The plasma source of claim 1 furthercomprising a third power supply that generates a third electric fieldacross the gap, the third electric field super-ionizing the initialplasma that is located in the gap.
 6. The plasma source of claim 1wherein the first and the second power supplies comprise a single powersupply that generates the first and the second electric fields.
 7. Theplasma source of claim 1 wherein the first and the second electricfields are chosen from the group comprising a static electric field, apulsed electric field, a quasi-static electric field, and an alternatingelectric field.
 8. The plasma source of claim 1 wherein the initialplasma comprises a weakly-ionized plasma.
 9. The plasma source of claim1 wherein the plasma comprising the higher density of ions comprises astrongly-ionized plasma.
 10. The plasma source of claim 1 wherein thesuper-ionizing the initial plasma comprises converting at leastseventy-five percent of neutral atoms in the initial plasma to ions. 11.The plasma source of claim 1 wherein the first electric field generatesexcited atoms in the initial plasma and generates secondary electronsfrom the outer cathode section, the secondary electrons ionizing theexcited atoms, thereby creating a plasma comprising a higher density ofions than the initial plasma.
 12. The plasma source of claim 1 furthercomprising a gas valve that controls the flow of feed gas so as toexchange the initial plasma with a second volume of feed gas as thefirst power supply generates the first electric field across the secondvolume of feed gas, thereby increasing an ion density of the plasma. 13.The plasma source of claim 1 further comprising a gas valve that injectsfeed gas between the outer cathode section and the anode at apredetermined time.
 14. The plasma source of claim 1 wherein at leastone of the first and the second power supplies generates the first andthe second electric fields, respectively, with a constant power.
 15. Theplasma source of claim 1 wherein at least one of the first and thesecond power supplies generates the first and the second electricfields, respectively, with a constant voltage.
 16. The plasma source ofclaim 1 wherein at least one of the first and the second power suppliesgenerates the first and the second electric fields, respectively, with aconstant current.
 17. The plasma source of claim 1 further comprising amagnet assembly that is positioned to generate a magnetic fieldproximate to at least one of the inner and the outer cathode sections,the magnetic field trapping electrons in at least one of the initialplasma and the plasma comprising the higher density of ions.
 18. Theplasma source of claim 17 wherein the magnet assembly comprises aplurality of magnets that generate magnetic field lines that aresubstantially parallel to at least one of the inner and the outercathode sections.
 19. The plasma source of claim 1 wherein at least oneof the inner and the outer cathode sections comprises a target materialthat is used for sputtering.
 20. A method of generating a high-densityplasma, the method comprising: generating a first electric field acrossa gap between an anode and an outer cathode section, the first electricfield ionizing a volume of feed gas that is located in the gap, therebygenerating an initial plasma in the gap; exchanging the initial plasmawith a second volume of feed gas while applying the first electric fieldacross the gap, thereby generating an additional plasma in the gap; andgenerating a second electric field proximate to the inner cathodesection, the second electric field super-ionizing the initial plasma,thereby generating a plasma comprising a higher density of ions than theinitial plasma.
 21. The method of claim 20 wherein the generating thefirst electric field across the gap comprises generating excited atomsin the initial plasma and generating secondary electrons from the outercathode section, the secondary electrons ionizing the excited atoms,thereby creating a plasma comprising a higher density of ions than theinitial plasma.
 22. The method of claim 20 wherein the first and thesecond electric fields are chosen from the group comprising a staticelectric field, a quasi-static electric field, a pulsed electric field,and an alternating electric field.
 23. The method of claim 20 whereinthe peak ion density of the initial plasma is between about 10⁷ cm⁻³ and10¹² cm⁻³.
 24. The method of claim 20 wherein the peak ion density ofthe plasma comprising the higher density of ions is greater than about10¹² cm⁻³.
 25. The method of claim 20 wherein the super-ionizing theinitial plasma comprises converting at least seventy-five percent ofneutral atoms in the initial plasma to ions.
 26. The method of claim 20further comprising generating a magnetic field proximate to at least oneof the inner and outer cathode sections, the magnetic field trappingelectrons in at least one of the initial plasma and the plasmacomprising the higher density of ions.
 27. The method of claim 26wherein the magnetic field comprises magnetic field lines that aresubstantially parallel to at least one of the inner and the outercathode sections.
 28. The method of claim 20 wherein the presence of theinitial plasma reduces a probability of developing an electricalbreakdown condition proximate to the inner cathode section as the secondelectric field is generated.
 29. The method of claim 20 furthercomprising exposing a substrate to the plasma comprising the higherdensity of ions, thereby etching a surface of the substrate.
 30. Asegmented cathode assembly for generating a high-density plasma, thesegmented cathode assembly comprising: an inner cathode section; anouter cathode section that surrounds the inner cathode section; and afirst anode that is positioned adjacent to the outer cathode section andforming a gap there between.
 31. The segmented cathode assembly of claim30 further comprising a second anode that surrounds the inner cathodesection.
 32. The segmented cathode assembly of claim 30 furthercomprising a magnet assembly that is positioned to generate a magneticfield proximate to at least one of the inner and the outer cathodesections.
 33. The segmented cathode assembly of claim 32 wherein themagnet assembly is rotatable.
 34. The segmented cathode assembly ofclaim 32 wherein the magnet assembly comprises a plurality of magnetsthat generate magnetic field lines that are substantially parallel to atleast one of the inner and the outer cathode sections.
 35. The segmentedcathode assembly of claim 30 wherein at least one of the inner and theouter cathode sections comprises a target material that is used forsputtering.
 36. The segmented cathode assembly of claim 30 furthercomprising at least one gas valve that injects feed gas into the gap ata predetermined time.
 37. The segmented cathode assembly of claim 31further comprising at least one gas valve that injects feed gas betweenthe inner cathode section and the second anode at a predetermined time.38. A method of generating a high-density plasma, the method comprising:ionizing a volume of feed gas that is located in a gap between an anodeand an outer cathode section to generate an initial plasma; transportingthe initial plasma proximate to an inner cathode section; andsuper-ionizing the initial plasma that is located proximate to the innercathode section, thereby generating a plasma comprising a higher densityof ions than the initial plasma.
 39. The method of claim 38 wherein theionizing a volume of feed gas comprises applying an electric fieldacross the volume of feed gas.
 40. The method of claim 38 wherein thesuper-ionizing the initial plasma comprises applying an electric fieldacross the initial plasma.
 41. The method of claim 38 wherein the peakion density of the initial plasma is between about 10⁷ cm⁻³ and 10¹²cm⁻³.
 42. The method of claim 38 wherein the peak ion density of theplasma comprising the higher density of ions is greater than about 10¹²cm⁻³.
 43. The method of claim 38 wherein the super-ionizing the initialplasma comprises converting at least seventy-five percent of neutralatoms in the initial plasma to ions.
 44. The method of claim 38 whereinthe transporting the initial plasma proximate to the inner cathodesection comprises exchanging the initial plasma with a second volume offeed gas.
 45. A plasma source comprising: means for generating a firstelectric field across a gap between an anode and an outer cathodesection, the first electric field ionizing a volume of feed gas that islocated in the gap, thereby generating an initial plasma in the gap;means for exchanging the initial plasma with a second volume of feed gaswhile applying the first electric field across the gap, therebygenerating an additional plasma in the gap; and means for generating asecond electric field proximate to an inner cathode section, the secondelectric field super-ionizing the initial plasma, thereby generating aplasma comprising a higher density of ions than the initial plasma. 46.A plasma source comprising: means for ionizing a volume of feed gas thatis located in a gap between an anode and an outer cathode section togenerate an initial plasma; means for transporting the initial plasmaproximate to an inner cathode section; and means for super-ionizing theinitial plasma that is located proximate to the inner cathode section,thereby generating a plasma comprising a higher density of ions than theinitial plasma.